diff --git a/CHANGELOG.md b/CHANGELOG.md
index 781afe4..98bbdf1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 This project uses [Semantic Versioning](https://semver.org).
 
+## [0.2.20] - 2026-06-14
+
+### Added
+
+- **`glint explain <RULE>`** — new subcommand that prints the description, rationale, a bad-YAML example, and the corrected fix for any rule ID (GL001–GL043). `glint explain` with no argument lists all rules with ID, severity, and title. Rule IDs are case-insensitive (`gl007` and `GL007` are equivalent).
+
+- **`rules:if:` evaluated reachability (GL042)** — warns when every `rules:if:` condition in a job evaluates to false using the values of variables declared in the pipeline YAML, meaning the job can never be included in a pipeline run. The check is conservative: it only fires when all variables referenced in the `if:` expressions are explicitly declared in the YAML; predefined `CI_*` / `GITLAB_*` variables and undeclared variables are treated as unknown (may have any runtime value) to avoid false positives.
+
+- **`inherit:` completeness (GL043)** — warns when a job declares `inherit: default:` (boolean or list form) but the pipeline has no `default:` block, making the declaration a no-op. Also warns when the list form names fields (e.g. `[image, before_script]`) that are not actually set in the `default:` block — those list entries have no effect.
+
 ## [0.2.19] - 2026-06-14
 
 ### Added
diff --git a/README.md b/README.md
index a649be3..ae989e4 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,7 @@
 
 <p align="center">
   <a href="LICENSE"><img src="https://img.shields.io/badge/license-Apache%202.0-blue.svg" alt="License"></a>
-  <a href="CHANGELOG.md"><img src="https://img.shields.io/badge/release-v0.2.19-blue.svg" alt="Release"></a>
+  <a href="CHANGELOG.md"><img src="https://img.shields.io/badge/release-v0.2.20-blue.svg" alt="Release"></a>
 </p>
 
 > **Disclaimer:** This tool was built through iterative AI-assisted development with [Claude](https://claude.ai). It is experimental, incomplete, and not intended for production use. Coverage of GitLab CI keywords is best-effort and may lag behind GitLab's evolving spec. Use it at your own discretion — no correctness guarantees are made. Contributions and bug reports are welcome.
@@ -39,6 +39,9 @@ A local tool to validate and lint `.gitlab-ci.yml` pipelines without needing a G
 - **`pages:` keyword + `artifacts.paths` (GL039)** — warns when a job uses the `pages:` keyword but `artifacts.paths` does not include the publish directory (default: `public`)
 - **Duplicate stage names (GL040)** — warns when a stage name appears more than once in `stages:`; GitLab silently merges duplicates, which can cause confusing ordering
 - **`cache.key.files` glob detection (GL041)** — warns when `cache.key.files` entries contain glob metacharacters; this field requires exact file paths, not patterns
+- **`rules:if:` evaluated reachability (GL042)** — warns when every `rules:if:` condition in a job evaluates to false using the values of variables declared in the pipeline YAML, making the job statically unreachable; only fires when all referenced variables are declared (predefined `CI_*` vars are excluded to avoid false positives)
+- **`inherit:` completeness (GL043)** — warns when `inherit: default:` is declared but the pipeline has no `default:` block (dead declaration), or when the list form names fields not set in the `default:` block
+- **`glint explain <RULE>`** — new subcommand that prints the rule description, rationale, a bad-YAML example, and the corrected fix; `glint explain` (no argument) lists all rules with their severity
 - **Recursive include depth limit** — include chains are capped at 100 nesting levels (matching GitLab's own limit); project and component includes are now tracked in the visited-file set to prevent cross-include cycles
 - **`include: inputs:` substitution** — when a `component:` entry has a `with:` block, all `$[[ inputs.KEY ]]` and `$[[ inputs.KEY | default(…) ]]` placeholders in the fetched template are substituted before parsing, so component-scoped jobs get their correct `stage:` and keyword values instead of `$[[…]]` placeholders
 - **Offline mode + include cache** — pass `--cache-dir DIR` to cache fetched remote templates (project: and component: includes) to disk; `--offline` serves entirely from the cache without making network calls
@@ -321,6 +324,21 @@ Jobs are colour-coded by type:
 DAG mode (job-to-job Bézier arrows) activates automatically when any job has a `needs:` list.
 Classic mode draws L-shaped or straight connectors between stage columns otherwise.
 
+### `glint explain`
+
+Print the documentation for a specific lint rule.
+
+```bash
+# Show description, example, and fix for GL007
+glint explain GL007
+
+# Case-insensitive: gl007 and GL007 are equivalent
+glint explain gl007
+
+# List all rules with their IDs and severity
+glint explain
+```
+
 ### Context simulation
 
 Pass `--branch`, `--tag`, or `--source` to `glint check` to see which jobs
@@ -462,6 +480,8 @@ Every finding includes a stable rule ID (e.g. `GL003`) that can be used to filte
 | GL032 | WARNING | `rules:if:` references `$VAR` not declared in `variables:` (pipeline, job, or `workflow:rules:variables:`) — may be a false positive for variables set in GitLab CI/CD project settings |
 | GL033 | WARNING | Every rule in `rules:` has `when: never` — job is permanently excluded from the pipeline (statically provable without context) |
 | GL035 | WARNING | `rules:changes` / `rules:exists` path is absolute; GitLab CI paths are relative to the repo root — absolute paths will never match |
+| GL042 | WARNING | Every `rules:if:` condition evaluates to false given the declared pipeline variable values — job can never be active (only fires when all referenced variables are declared in YAML) |
+| GL043 | WARNING | `inherit: default:` is declared but there is no `default:` block in the pipeline, or the list form names fields not set in `default:` — declaration has no effect |
 
 ### Hidden jobs (templates)
 
diff --git a/ROADMAP.md b/ROADMAP.md
index 3f20d23..fd8fe3c 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -4,53 +4,25 @@ This document tracks planned improvements to `glint`. Items are grouped by theme
 
 ---
 
-## Context-aware validation — ✓ single-context shipped in v0.2.0; expression evaluator hardened post-v0.2.0; implicit defaults and --list-vars shipped v0.2.11; variable expansion and scalar handling shipped v0.2.13; workflow evaluation and output fixes shipped v0.2.14
+## Context simulation
 
-Single-context simulation is fully implemented. Pass `--branch`, `--tag`, `--source`, or `--var` to either `glint check` or `glint graph`; jobs are evaluated and shown as active / manual / skipped.
+Pass `--branch`, `--tag`, `--source`, or `--var` to `glint check` or `glint graph` to evaluate `rules:if:` expressions and `only`/`except` filters against a specific pipeline event.
 
-```bash
-# shipped: single-context simulation
-glint check --branch develop .gitlab-ci.yml
-glint check --tag v1.2.0 .gitlab-ci.yml
-glint check --source merge_request_event --var CI_MERGE_REQUEST_TARGET_BRANCH_NAME=main .gitlab-ci.yml
-glint graph tree --branch main .gitlab-ci.yml   # tree annotated with [skipped] / [manual]
-```
-
-**Shipped post-v0.2.0 (unreleased)**
-
-- ✓ **`workflow:rules:variables:` propagation** — variables defined on the matching `workflow:rules:` entry are injected into the evaluation context before job `rules:if:` expressions are evaluated. Pipeline-level `variables:` defaults are also available. Priority chain (highest wins): `--var` > shortcuts > workflow-rule vars > pipeline defaults.
-- ✓ **Expression evaluator: multi-line expressions** — newlines in block-scalar and folded YAML `if:` values are now treated as whitespace; `||` / `&&` on a continuation line evaluate correctly.
-- ✓ **Expression evaluator: `${VAR}` curly-brace syntax** — `${CI_COMMIT_BRANCH}` is equivalent to `$CI_COMMIT_BRANCH` everywhere.
-- ✓ **Expression evaluator: regex flags** — `/pattern/i`, `/pattern/m`, `/pattern/s` are now supported; `i` maps to `(?i)` in Go's regexp.
-- ✓ **Expression evaluator: variable as regex RHS** — `$BRANCH =~ $PATTERN` where `$PATTERN` holds a `/regex/` string is evaluated correctly.
-- ✓ **Expression evaluator: bare `true` / `false` keywords** — treated as the strings `"true"` / `"false"` matching GitLab CI's own behaviour; `$GATEWAY_ENABLED == true` now evaluates correctly.
-- ✓ **Expression evaluator: integer literals** — `$COUNT == 4`, `$ENABLED == 1`, `$DISABLED == 0` compare as decimal strings.
-
-~~**Implicit default context**~~ — ✓ shipped v0.2.11; `glint check` and `glint graph` default to `--branch main --source push` when no context flag is given, so `rules:if:` expressions are always evaluated out of the box.
-
-~~**`--list-vars` debug flag**~~ — ✓ shipped v0.2.11; prints sorted `KEY=VALUE` of all collected variables (pipeline YAML + included files + workflow-rule union + effective context) to stderr.
-
-**Shipped in v0.2.13**
-
-- ✓ **Variable expansion** — `$VAR` / `${VAR}` references within variable values are expanded after all sources are merged; transitive chains resolve over multiple passes; visible in `--list-vars` effective-context output.
-- ✓ **Non-string scalar variables** — `BUILD: true`, `RETRIES: 3` and similar bare boolean/integer values now render correctly in `--list-vars` and are injected into the evaluation context as string equivalents; previously shown as `(complex)` and silently dropped.
-- ✓ **YAML `\/` escape in double-quoted strings** — regex patterns like `/^us\//` in double-quoted `if:` blocks no longer cause a parse error; the raw bytes are preprocessed before YAML unmarshalling.
-
-**Shipped in v0.2.14**
-
-- ✓ **Workflow rule strict evaluation** — workflow `rules:if:` now uses strict mode (parse failure → skip rule, not match); fixes premature matching that blocked later rules and injected wrong variables.
-- ✓ **Single `=` operator** — `=` is now accepted as an alias for `==` in `rules:if:` expressions, matching common user intent.
-- ✓ **Source location through `extends:` resolution** — `File` and `Line` are now preserved when a job is rebuilt via extends, so findings reference the correct source location.
-- ✓ **Sorted findings output** — findings are sorted by `(File, Line, Rule)`; same-file issues group together in line order.
-- ✓ **Consistent warning format** — all warnings use ruff-style `path: [warning] message` format.
-- ✓ **`--version` / `-v` flag** — prints compiled version; version also shown at the top of every `--help` output.
-
-**Remaining work**
-
-- **Multi-context simulation** — run multiple contexts in one invocation and print a comparison table:
-  ```bash
-  glint check --context branch=main --context branch=develop --context tag=v1.0.0 .gitlab-ci.yml
-  ```
+- ~~**Single-context simulation**~~ — ✓ shipped v0.2.0; `--branch`, `--tag`, `--source`, `--var` flags on both subcommands; jobs classified as active / manual / skipped
+- ~~**`workflow:rules:variables:` propagation**~~ — ✓ shipped post-v0.2.0; variables from the matching workflow rule entry injected into the evaluation context before job `rules:if:` expressions are evaluated
+- ~~**Expression evaluator: multi-line `if:` values**~~ — ✓ shipped post-v0.2.0; newlines in block-scalar and folded YAML `if:` values treated as whitespace
+- ~~**Expression evaluator: `${VAR}` syntax**~~ — ✓ shipped post-v0.2.0; `${CI_COMMIT_BRANCH}` equivalent to `$CI_COMMIT_BRANCH` everywhere
+- ~~**Expression evaluator: regex flags**~~ — ✓ shipped post-v0.2.0; `/pattern/i`, `/pattern/m`, `/pattern/s` supported
+- ~~**Expression evaluator: variable as regex RHS**~~ — ✓ shipped post-v0.2.0; `$BRANCH =~ $PATTERN` where `$PATTERN` holds a `/regex/` string evaluates correctly
+- ~~**Expression evaluator: bare `true`/`false` and integer literals**~~ — ✓ shipped post-v0.2.0; `$FLAG == true`, `$COUNT == 4` compare as decimal strings matching GitLab CI behaviour
+- ~~**Implicit default context**~~ — ✓ shipped v0.2.11; defaults to `--branch main --source push` when no context flag is given, so `rules:if:` is always evaluated
+- ~~**`--list-vars` debug flag**~~ — ✓ shipped v0.2.11; prints sorted `KEY=VALUE` of all collected pipeline variables (root file + includes + workflow-rule union + effective context) to stderr
+- ~~**Variable expansion**~~ — ✓ shipped v0.2.13; `$VAR`/`${VAR}` references within variable values expanded after all sources are merged; transitive chains resolved; visible in `--list-vars`
+- ~~**Non-string scalar variables**~~ — ✓ shipped v0.2.13; `BUILD: true`, `RETRIES: 3` rendered and injected correctly instead of being silently dropped
+- ~~**YAML `\/` escape in double-quoted strings**~~ — ✓ shipped v0.2.13; regex patterns like `/^us\//` in double-quoted `if:` blocks no longer cause a parse error
+- ~~**Workflow rule strict evaluation**~~ — ✓ shipped v0.2.14; unparseable `if:` skips the rule instead of matching everything; prevents wrong variables being injected
+- ~~**Single `=` operator**~~ — ✓ shipped v0.2.14; bare `=` accepted as alias for `==` in `rules:if:` expressions
+- **Multi-context simulation** — run multiple contexts in one invocation and print a comparison table (`--context branch=main --context branch=develop --context tag=v1.0.0`)
 - **Context-scoped linting** — skip `needs:`/`dependencies:` cross-checks for jobs that are statically unreachable in the given context
 - **`rules:changes:` evaluation** — path glob evaluation against the local git tree
 
@@ -70,7 +42,7 @@ The current rule set covers the most common sources of broken pipelines. These a
 - ~~**Duplicate stage names (GL040)**~~ — ✓ shipped v0.2.16; warns when a stage appears more than once in `stages:`
 - ~~**`cache:key:files` must be exact paths (GL041)**~~ — ✓ shipped v0.2.16; warns when entries look like glob patterns
 - ~~**Unreachable jobs**~~ — covered by GL033 (shipped v0.2.15); every-`when:never` rules block is statically dead
-- **`inherit:` completeness** — flag when a job overrides a default field that would require `inherit: default: false` to suppress
+- ~~**`inherit:` completeness (GL043)**~~ — ✓ shipped v0.2.20; warns when `inherit: default:` is declared but there's no `default:` block, or list form names fields not set in `default:`
 
 ---
 
@@ -118,7 +90,7 @@ The SVG renderer and terminal tree cover the basic layout. These would bring it
 
 - ~~**`needs: optional: true` false-positive errors**~~ — ✓ shipped post-v0.2.0; optional missing needs are downgraded to `[WARNING]`
 - ~~**`extends:` jobs with missing script false errors**~~ — ✓ shipped post-v0.2.0; jobs using `extends:` that have no `script` after resolution emit `[WARNING]` (the script may come from an unfetchable remote base)
-- **`rules:if:` static reachability** — report when a job's entire `rules:` block can never evaluate to `when: on_success` given the declared pipeline variables (pure static, no context required)
+- ~~**`rules:if:` static reachability (GL042)**~~ — ✓ shipped v0.2.20; warns when all `rules:if:` conditions evaluate to false given declared variable values (only fires when all referenced vars are declared in YAML)
 
 ---
 
@@ -141,8 +113,8 @@ The SVG renderer and terminal tree cover the basic layout. These would bring it
 
 ## Reliability and developer experience
 
-- ~~**Structured rule IDs**~~ — ✓ shipped post-v0.2.0; GL001–GL031 assigned; GL032 added v0.2.11; GL033 added v0.2.15; GL034–GL041 added v0.2.16; output formats (--format json/sarif/junit/github) added v0.2.18
-- **`--explain <rule-id>`** — print the rule description, rationale, and an example fix
+- ~~**Structured rule IDs**~~ — ✓ shipped post-v0.2.0; GL001–GL031 assigned; GL032 added v0.2.11; GL033 added v0.2.15; GL034–GL041 added v0.2.16; output formats (--format json/sarif/junit/github) added v0.2.18; GL042–GL043 added v0.2.20
+- ~~**`glint explain <rule-id>`**~~ — ✓ shipped v0.2.20; prints rule description, rationale, bad-YAML example, and fix; `glint explain` (no arg) lists all rules
 - ~~**Semantic versioning and first release**~~ — shipped as `v0.1.0` (2026-06-07)
 - ~~**Subcommand CLI**~~ — shipped as `v0.2.0` (2026-06-11); `glint check` / `glint graph [mode]` with ruff-style `--help`
 - **Changelog automation** — generate release notes from Conventional Commits via `git-cliff` or similar
diff --git a/Taskfile.yml b/Taskfile.yml
index 228cfe6..ae1d576 100644
--- a/Taskfile.yml
+++ b/Taskfile.yml
@@ -107,6 +107,18 @@ tasks:
         ignore_error: false
       - cmd: ./{{.BINARY}} check testdata/config_suppress/.gitlab-ci.yml
         ignore_error: false
+      - cmd: ./{{.BINARY}} check testdata/static_dead_rules.yml
+        ignore_error: false
+      - cmd: ./{{.BINARY}} check testdata/inherit_dead.yml
+        ignore_error: false
+      - cmd: ./{{.BINARY}} check testdata/inherit_dead_fields.yml
+        ignore_error: false
+      - cmd: ./{{.BINARY}} explain GL007
+        ignore_error: false
+      - cmd: ./{{.BINARY}} explain gl042
+        ignore_error: false
+      - cmd: ./{{.BINARY}} explain
+        ignore_error: false
 
   lint-go:
     desc: Run go vet on all packages
diff --git a/cmd/glint/explain.go b/cmd/glint/explain.go
new file mode 100644
index 0000000..bafbe5a
--- /dev/null
+++ b/cmd/glint/explain.go
@@ -0,0 +1,69 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+
+	"git.k3nny.fr/glint/internal/linter"
+)
+
+func cmdExplain(args []string) {
+	if len(args) == 0 {
+		printRuleList()
+		return
+	}
+	ruleID := strings.ToUpper(args[0])
+	entry, ok := linter.RuleCatalog[ruleID]
+	if !ok {
+		fmt.Fprintf(os.Stderr, "glint explain: unknown rule %q\n\nRun 'glint explain' to list all rules.\n", ruleID)
+		os.Exit(2)
+	}
+	printRuleEntry(ruleID, entry)
+}
+
+func printRuleEntry(id string, e linter.RuleEntry) {
+	sev := strings.ToLower(string(e.Severity))
+	header := fmt.Sprintf("%s  [%s]  %s", id, sev, e.Title)
+	rule := fmt.Sprintf("\n%s\n%s\n\n%s\n",
+		header,
+		strings.Repeat("─", len(header)),
+		e.Description,
+	)
+	fmt.Print(rule)
+
+	if e.Example != "" {
+		fmt.Println("Example:")
+		fmt.Println()
+		for _, line := range strings.Split(e.Example, "\n") {
+			fmt.Printf("  %s\n", line)
+		}
+		fmt.Println()
+	}
+
+	if e.Fix != "" {
+		fmt.Println("Fix:")
+		fmt.Println()
+		for _, line := range strings.Split(e.Fix, "\n") {
+			fmt.Printf("  %s\n", line)
+		}
+		fmt.Println()
+	}
+}
+
+func printRuleList() {
+	ids := make([]string, 0, len(linter.RuleCatalog))
+	for id := range linter.RuleCatalog {
+		ids = append(ids, id)
+	}
+	sort.Strings(ids)
+
+	fmt.Printf("glint %s — lint rules\n\n", version)
+	for _, id := range ids {
+		e := linter.RuleCatalog[id]
+		sev := strings.ToLower(string(e.Severity))
+		fmt.Printf("  %-6s  [%-7s]  %s\n", id, sev, e.Title)
+	}
+	fmt.Println("\nUse 'glint explain <RULE>' for details on a specific rule.")
+}
diff --git a/cmd/glint/main.go b/cmd/glint/main.go
index 7af60e0..ba71e14 100644
--- a/cmd/glint/main.go
+++ b/cmd/glint/main.go
@@ -39,6 +39,7 @@ Usage: glint [OPTIONS] <COMMAND>
 Commands:
   check    Lint a pipeline file — exits 0 (clean) or 1 (errors found)
   graph    Visualise the pipeline as a job tree or Mermaid graph
+  explain  Show description and fix for a lint rule (e.g. glint explain GL007)
 
 Options:
   -h, --help     Print help
@@ -57,6 +58,8 @@ func main() {
 		cmdCheck(os.Args[2:])
 	case "graph":
 		cmdGraph(os.Args[2:])
+	case "explain":
+		cmdExplain(os.Args[2:])
 	case "-h", "--help", "help":
 		fmt.Fprintf(os.Stderr, "glint %s\n\n", version)
 		fmt.Fprint(os.Stderr, globalUsage)
diff --git a/internal/linter/explain.go b/internal/linter/explain.go
new file mode 100644
index 0000000..0d7b8cf
--- /dev/null
+++ b/internal/linter/explain.go
@@ -0,0 +1,819 @@
+package linter
+
+// RuleEntry holds the human-readable documentation for a single lint rule,
+// shown by 'glint explain <RULE>'.
+type RuleEntry struct {
+	Title       string   // short title (one line)
+	Severity    Severity // Error or Warning
+	Description string   // what triggers the rule and why it matters
+	Example     string   // YAML snippet that triggers the rule
+	Fix         string   // corrected YAML
+}
+
+// RuleCatalog maps stable rule IDs to their documentation entries.
+var RuleCatalog = map[string]RuleEntry{
+	RuleNoStages: {
+		Title:    "no stages defined",
+		Severity: Warning,
+		Description: "The pipeline has no 'stages:' block. GitLab falls back to the " +
+			"built-in default stages (build, test, deploy), which may not match your " +
+			"intended job ordering.",
+		Example: `# No stages: block
+build-job:
+  script: make build
+
+test-job:
+  script: make test`,
+		Fix: `stages:
+  - build
+  - test
+
+build-job:
+  stage: build
+  script: make build
+
+test-job:
+  stage: test
+  script: make test`,
+	},
+
+	RuleWorkflowWhen: {
+		Title:    "workflow.rules.when invalid value",
+		Severity: Error,
+		Description: "'workflow.rules[n].when' only accepts 'always' or 'never'. Any " +
+			"other value (such as 'on_success' or 'manual') is invalid and will cause " +
+			"the pipeline to fail to create.",
+		Example: `workflow:
+  rules:
+    - if: $CI_COMMIT_BRANCH
+      when: on_success   # invalid here`,
+		Fix: `workflow:
+  rules:
+    - if: $CI_COMMIT_BRANCH
+      when: always`,
+	},
+
+	RuleMissingScript: {
+		Title:    "missing required 'script' field",
+		Severity: Error,
+		Description: "Every non-trigger, non-pages job must define 'script:' (or 'run:' " +
+			"for CI Steps). A job with no script will fail immediately when GitLab tries " +
+			"to run it.",
+		Example: `my-job:
+  stage: test
+  image: python:3.12
+  # Missing script:`,
+		Fix: `my-job:
+  stage: test
+  image: python:3.12
+  script: pytest`,
+	},
+
+	RuleUnknownStage: {
+		Title:    "job references undeclared stage",
+		Severity: Error,
+		Description: "The job's 'stage:' value does not match any name in the pipeline's " +
+			"'stages:' list. GitLab will reject the pipeline configuration.",
+		Example: `stages:
+  - build
+  - test
+
+deploy-job:
+  stage: production   # not in stages:
+  script: ./deploy.sh`,
+		Fix: `stages:
+  - build
+  - test
+  - production
+
+deploy-job:
+  stage: production
+  script: ./deploy.sh`,
+	},
+
+	RuleOnlyRulesConflict: {
+		Title:    "'only:' and 'rules:' used together",
+		Severity: Error,
+		Description: "'only:' and 'rules:' are mutually exclusive. Using both on the " +
+			"same job is a configuration error that prevents the pipeline from being " +
+			"created.",
+		Example: `my-job:
+  only:
+    - main
+  rules:
+    - if: $CI_COMMIT_BRANCH
+  script: echo conflict`,
+		Fix: `# Remove only: and use rules: exclusively
+my-job:
+  rules:
+    - if: $CI_COMMIT_BRANCH == "main"
+  script: echo ok`,
+	},
+
+	RuleExceptRulesConflict: {
+		Title:    "'except:' and 'rules:' used together",
+		Severity: Error,
+		Description: "'except:' and 'rules:' are mutually exclusive. Using both on the " +
+			"same job is a configuration error that prevents the pipeline from being " +
+			"created.",
+		Example: `my-job:
+  except:
+    - tags
+  rules:
+    - if: $CI_COMMIT_BRANCH
+  script: echo conflict`,
+		Fix: `my-job:
+  rules:
+    - if: $CI_COMMIT_TAG
+      when: never
+    - if: $CI_COMMIT_BRANCH
+  script: echo ok`,
+	},
+
+	RuleDeprecatedOnly: {
+		Title:    "'only:' / 'except:' deprecated",
+		Severity: Warning,
+		Description: "'only:' and 'except:' are deprecated in favour of 'rules:'. " +
+			"GitLab may remove support for these keywords in a future major version. " +
+			"'rules:' is more expressive and supports variable references, merge-request " +
+			"conditions, and fine-grained 'when:' control.",
+		Example: `my-job:
+  only:
+    - main
+  script: ./deploy.sh`,
+		Fix: `my-job:
+  rules:
+    - if: $CI_COMMIT_BRANCH == "main"
+  script: ./deploy.sh`,
+	},
+
+	RuleInvalidWhen: {
+		Title:    "'when:' has invalid value",
+		Severity: Error,
+		Description: "Job-level 'when:' accepts: on_success, on_failure, always, " +
+			"manual, delayed, never. Any other value is rejected by GitLab.",
+		Example: `my-job:
+  when: sometimes   # invalid
+  script: echo hi`,
+		Fix: `my-job:
+  when: on_success
+  script: echo hi`,
+	},
+
+	RuleDelayedNoStartIn: {
+		Title:    "'when: delayed' without 'start_in:'",
+		Severity: Error,
+		Description: "'when: delayed' requires a 'start_in:' duration (e.g. " +
+			"'30 minutes', '1 hour'). Without it GitLab rejects the job configuration.",
+		Example: `my-job:
+  when: delayed
+  script: echo hi`,
+		Fix: `my-job:
+  when: delayed
+  start_in: 30 minutes
+  script: echo hi`,
+	},
+
+	RuleStartInNoDelayed: {
+		Title:    "'start_in:' without 'when: delayed'",
+		Severity: Error,
+		Description: "'start_in:' is only meaningful when 'when: delayed'. Setting it " +
+			"alongside any other 'when:' value is a configuration error.",
+		Example: `my-job:
+  when: on_success
+  start_in: 30 minutes   # only valid with delayed
+  script: echo hi`,
+		Fix: `my-job:
+  when: delayed
+  start_in: 30 minutes
+  script: echo hi`,
+	},
+
+	RuleInvalidParallel: {
+		Title:    "'parallel:' value invalid",
+		Severity: Error,
+		Description: "'parallel:' must be an integer between 2 and 200 (inclusive), " +
+			"or a map with a 'matrix:' key for matrix jobs. Values outside this range " +
+			"or the wrong type are rejected by GitLab.",
+		Example: `my-job:
+  parallel: 1   # must be 2–200
+  script: echo hi`,
+		Fix: `my-job:
+  parallel: 5
+  script: echo hi`,
+	},
+
+	RuleInvalidRetry: {
+		Title:    "'retry:' value invalid",
+		Severity: Error,
+		Description: "'retry:' accepts an integer 0–2 or a map with optional 'max:' " +
+			"(0–2) and 'when:' keys. Values outside this range are rejected.",
+		Example: `my-job:
+  retry: 5   # max is 2
+  script: echo hi`,
+		Fix: `my-job:
+  retry: 2
+  script: echo hi`,
+	},
+
+	RuleInvalidRetryWhen: {
+		Title:    "'retry.when:' has invalid failure type",
+		Severity: Error,
+		Description: "'retry.when:' must be a recognised GitLab CI failure type " +
+			"(e.g. script_failure, runner_system_failure) or 'always'. Unknown " +
+			"values are rejected.",
+		Example: `my-job:
+  retry:
+    max: 2
+    when: disk_full   # not a valid failure type
+  script: echo hi`,
+		Fix: `my-job:
+  retry:
+    max: 2
+    when: runner_system_failure
+  script: echo hi`,
+	},
+
+	RuleInvalidAllowFailure: {
+		Title:    "'allow_failure:' invalid value",
+		Severity: Error,
+		Description: "'allow_failure:' must be a boolean (true/false) or a map with " +
+			"an 'exit_codes:' key. Other forms are rejected by GitLab.",
+		Example: `my-job:
+  allow_failure: maybe   # must be true/false or map
+  script: echo hi`,
+		Fix: `my-job:
+  allow_failure: true
+  script: echo hi`,
+	},
+
+	RuleInvalidInterruptible: {
+		Title:    "'interruptible:' is not a boolean",
+		Severity: Error,
+		Description: "'interruptible:' must be a boolean (true or false). Other types " +
+			"are rejected.",
+		Example: `my-job:
+  interruptible: yes   # must be a YAML boolean true/false
+  script: echo hi`,
+		Fix: `my-job:
+  interruptible: true
+  script: echo hi`,
+	},
+
+	RuleTriggerWithScript: {
+		Title:    "trigger job also defines 'script:'",
+		Severity: Error,
+		Description: "Jobs with a 'trigger:' key (downstream pipeline triggers) cannot " +
+			"use 'script:'. These are mutually exclusive — a trigger job has no runner " +
+			"environment to execute scripts in.",
+		Example: `trigger-job:
+  trigger:
+    project: mygroup/myproject
+  script: echo this will fail`,
+		Fix: `trigger-job:
+  trigger:
+    project: mygroup/myproject`,
+	},
+
+	RuleInvalidTrigger: {
+		Title:    "trigger: map missing 'project:' or 'include:'",
+		Severity: Error,
+		Description: "When 'trigger:' is a map it must specify either 'project:' " +
+			"(downstream project trigger) or 'include:' (dynamic child pipeline). " +
+			"Without one of these keys GitLab cannot determine what to trigger.",
+		Example: `trigger-job:
+  trigger:
+    strategy: depend   # missing project: or include:`,
+		Fix: `trigger-job:
+  trigger:
+    project: mygroup/downstream
+    strategy: depend`,
+	},
+
+	RuleInvalidCoverage: {
+		Title:    "'coverage:' is not a regex pattern",
+		Severity: Error,
+		Description: "'coverage:' must be a regex pattern wrapped in forward slashes " +
+			"(e.g. '/Coverage: \\d+\\.?\\d*%/'). GitLab uses this pattern to extract " +
+			"the coverage percentage from job output.",
+		Example: `my-job:
+  coverage: "\\d+%"   # missing surrounding /…/
+  script: pytest --cov`,
+		Fix: `my-job:
+  coverage: '/Coverage: \d+\.?\d*%/'
+  script: pytest --cov`,
+	},
+
+	RuleInvalidRelease: {
+		Title:    "'release:' missing required 'tag_name:'",
+		Severity: Error,
+		Description: "'release:' must be a map and must include a 'tag_name:' key. " +
+			"Without it GitLab cannot create the release.",
+		Example: `release-job:
+  script: echo releasing
+  release:
+    name: My Release   # missing tag_name:`,
+		Fix: `release-job:
+  script: echo releasing
+  release:
+    tag_name: $CI_COMMIT_TAG
+    name: My Release`,
+	},
+
+	RuleInvalidEnvironment: {
+		Title:    "'environment:' invalid url or action",
+		Severity: Error,
+		Description: "'environment.url' requires 'environment.name' to be set. " +
+			"'environment.action' must be one of: start, stop, prepare, verify, access.",
+		Example: `my-job:
+  script: ./deploy.sh
+  environment:
+    url: https://prod.example.com   # name: is required`,
+		Fix: `my-job:
+  script: ./deploy.sh
+  environment:
+    name: production
+    url: https://prod.example.com`,
+	},
+
+	RuleInvalidArtifacts: {
+		Title:    "'artifacts:' invalid configuration",
+		Severity: Error,
+		Description: "'artifacts.when' must be on_success, on_failure, or always. " +
+			"'artifacts.expose_as' requires 'artifacts.paths' to be set.",
+		Example: `my-job:
+  script: make
+  artifacts:
+    when: sometimes   # invalid value`,
+		Fix: `my-job:
+  script: make
+  artifacts:
+    when: on_failure
+    paths:
+      - build/logs/`,
+	},
+
+	RulePagesPublic: {
+		Title:    "pages job missing 'public' in artifacts.paths",
+		Severity: Warning,
+		Description: "The 'pages' job must include 'public' (or a path starting with " +
+			"'public/') in 'artifacts.paths' for GitLab Pages to deploy the site.",
+		Example: `pages:
+  script: hugo
+  artifacts:
+    paths:
+      - dist/   # should include public/`,
+		Fix: `pages:
+  script: hugo --destination public
+  artifacts:
+    paths:
+      - public/`,
+	},
+
+	RuleInvalidCache: {
+		Title:    "'cache:' invalid when or policy",
+		Severity: Error,
+		Description: "'cache.when' must be on_success, on_failure, or always. " +
+			"'cache.policy' must be pull, push, or pull-push.",
+		Example: `my-job:
+  script: npm ci
+  cache:
+    paths: [node_modules/]
+    policy: read-only   # invalid; use pull`,
+		Fix: `my-job:
+  script: npm ci
+  cache:
+    paths: [node_modules/]
+    policy: pull`,
+	},
+
+	RuleInvalidRulesWhen: {
+		Title:    "'rules[n].when:' has invalid value",
+		Severity: Error,
+		Description: "Inside a 'rules:' block, 'when:' must be one of: on_success, " +
+			"on_failure, always, manual, delayed, never. Other values are rejected.",
+		Example: `my-job:
+  rules:
+    - if: $CI_COMMIT_BRANCH
+      when: conditional   # not valid here
+  script: echo hi`,
+		Fix: `my-job:
+  rules:
+    - if: $CI_COMMIT_BRANCH
+      when: on_success
+  script: echo hi`,
+	},
+
+	RuleInvalidImage: {
+		Title:    "'image:' map form missing 'name:'",
+		Severity: Error,
+		Description: "When 'image:' is a map, it must include a 'name:' key specifying " +
+			"the Docker image. Without it GitLab cannot resolve which image to pull.",
+		Example: `my-job:
+  image:
+    entrypoint: ["/bin/sh"]   # missing name:
+  script: echo hi`,
+		Fix: `my-job:
+  image:
+    name: alpine:3.19
+    entrypoint: ["/bin/sh"]
+  script: echo hi`,
+	},
+
+	RuleInvalidInherit: {
+		Title:    "'inherit.default' or 'inherit.variables' invalid type",
+		Severity: Error,
+		Description: "'inherit.default' and 'inherit.variables' must each be a boolean " +
+			"(true/false) or a list of field/variable names. Other types are rejected.",
+		Example: `my-job:
+  inherit:
+    default: "no"   # must be true/false or a list
+  script: echo hi`,
+		Fix: `my-job:
+  inherit:
+    default: false
+  script: echo hi`,
+	},
+
+	RuleNeedsUnknown: {
+		Title:    "'needs:' references unknown job",
+		Severity: Error,
+		Description: "A job in the 'needs:' list does not exist in the pipeline. " +
+			"GitLab will refuse to create the pipeline.",
+		Example: `build:
+  stage: build
+  script: make
+
+test:
+  stage: test
+  needs: [build, lint]   # lint does not exist
+  script: make test`,
+		Fix: `lint:
+  stage: build
+  script: make lint
+
+build:
+  stage: build
+  script: make
+
+test:
+  stage: test
+  needs: [build, lint]
+  script: make test`,
+	},
+
+	RuleNeedsStageOrder: {
+		Title:    "'needs:' job is in a later stage",
+		Severity: Error,
+		Description: "A job listed in 'needs:' is in a later stage than the current " +
+			"job. GitLab does not allow needs: to reference future stages.",
+		Example: `stages: [build, test, deploy]
+
+test:
+  stage: test
+  needs: [deploy-job]   # deploy-job is in a later stage
+  script: make test
+
+deploy-job:
+  stage: deploy
+  script: ./deploy.sh`,
+		Fix: `stages: [build, test, deploy]
+
+test:
+  stage: test
+  needs: [build-job]
+  script: make test
+
+build-job:
+  stage: build
+  script: make`,
+	},
+
+	RuleNeedsCycle: {
+		Title:    "circular dependency in 'needs:' graph",
+		Severity: Error,
+		Description: "Two or more jobs in the 'needs:' graph form a cycle — A needs B " +
+			"and B needs A (directly or transitively). GitLab will reject the pipeline.",
+		Example: `job-a:
+  stage: test
+  needs: [job-b]
+  script: echo a
+
+job-b:
+  stage: test
+  needs: [job-a]
+  script: echo b`,
+		Fix: `job-a:
+  stage: test
+  script: echo a
+
+job-b:
+  stage: test
+  needs: [job-a]
+  script: echo b`,
+	},
+
+	RuleUnknownDependency: {
+		Title:    "'dependencies:' references unknown job",
+		Severity: Error,
+		Description: "A job listed in 'dependencies:' does not exist in the pipeline. " +
+			"GitLab will refuse to create the pipeline.",
+		Example: `test:
+  stage: test
+  dependencies: [build, missing-job]
+  script: make test`,
+		Fix: `build:
+  stage: build
+  script: make
+  artifacts:
+    paths: [dist/]
+
+test:
+  stage: test
+  dependencies: [build]
+  script: make test`,
+	},
+
+	RuleDependencyStage: {
+		Title:    "'dependencies:' job in same or later stage",
+		Severity: Error,
+		Description: "'dependencies:' can only reference jobs in earlier stages. " +
+			"Referencing a job in the same or a later stage is not allowed because " +
+			"artifacts would not yet be available.",
+		Example: `stages: [test, deploy]
+
+test:
+  stage: test
+  dependencies: [deploy-job]   # deploy is a later stage
+  script: make test
+
+deploy-job:
+  stage: deploy
+  script: ./deploy.sh`,
+		Fix: `stages: [build, test, deploy]
+
+build:
+  stage: build
+  script: make
+  artifacts:
+    paths: [dist/]
+
+test:
+  stage: test
+  dependencies: [build]
+  script: make test`,
+	},
+
+	RuleUndeclaredVariable: {
+		Title:    "'rules:if:' references undeclared variable",
+		Severity: Warning,
+		Description: "A 'rules:if:' expression references a variable that is not " +
+			"declared in any 'variables:' block in the pipeline YAML. This may be a " +
+			"typo, or the variable may be set in GitLab project settings (invisible to " +
+			"glint). Predefined CI_* and GITLAB_* variables are always exempt.",
+		Example: `variables:
+  APP_ENV: staging
+
+my-job:
+  rules:
+    - if: $DEPLOY_ENV == "prod"   # DEPLOY_ENV not declared
+  script: ./deploy.sh`,
+		Fix: `variables:
+  APP_ENV: staging
+  DEPLOY_ENV: staging   # declare it, or set it in GitLab project settings
+
+my-job:
+  rules:
+    - if: $DEPLOY_ENV == "prod"
+  script: ./deploy.sh`,
+	},
+
+	RuleDeadRules: {
+		Title:    "rules: block has all 'when: never' — job permanently excluded",
+		Severity: Warning,
+		Description: "Every rule in the job's 'rules:' block has an explicit " +
+			"'when: never'. No matter which conditions match, the job will never " +
+			"be included in any pipeline run.",
+		Example: `my-job:
+  rules:
+    - if: $CI_COMMIT_BRANCH == "main"
+      when: never
+    - when: never
+  script: echo unreachable`,
+		Fix: `# Option 1: remove the job entirely
+# Option 2: give at least one rule a non-never when:
+my-job:
+  rules:
+    - if: $CI_COMMIT_BRANCH == "main"
+      when: on_success
+    - when: never
+  script: echo deploy`,
+	},
+
+	RuleInvalidService: {
+		Title:    "'services:' map form missing 'name:' or invalid 'alias:'",
+		Severity: Error,
+		Description: "When a service entry is a map it must include a 'name:' key. " +
+			"'alias:' (if set) must be a valid DNS label: alphanumeric characters, " +
+			"hyphens, and dots only; must start and end with alphanumeric.",
+		Example: `my-job:
+  script: pytest
+  services:
+    - alias: my_db   # underscore is not valid in a DNS label`,
+		Fix: `my-job:
+  script: pytest
+  services:
+    - name: postgres:15
+      alias: my-db`,
+	},
+
+	RuleAbsoluteGlobPath: {
+		Title:    "'rules:changes' or 'rules:exists' uses absolute path",
+		Severity: Warning,
+		Description: "Paths in 'rules:changes' and 'rules:exists' are always relative " +
+			"to the repository root. An absolute path starting with '/' will never " +
+			"match any file and will silently disable the rule.",
+		Example: `my-job:
+  rules:
+    - changes:
+        - /src/**/*.go   # absolute — will never match
+  script: make`,
+		Fix: `my-job:
+  rules:
+    - changes:
+        - src/**/*.go
+  script: make`,
+	},
+
+	RuleInvalidTimeout: {
+		Title:    "'timeout:' is not a valid duration string",
+		Severity: Error,
+		Description: "'timeout:' must be a GitLab CI duration string composed of " +
+			"recognised time units: weeks (w), days (d), hours (h), minutes (m/min), " +
+			"seconds (s). Examples: '1h 30m', '90 minutes', '2 hours'.",
+		Example: `my-job:
+  timeout: "1:30:00"   # colon-separated format not supported
+  script: long-running-task.sh`,
+		Fix: `my-job:
+  timeout: 1h 30m
+  script: long-running-task.sh`,
+	},
+
+	RuleInvalidIDToken: {
+		Title:    "'id_tokens:' entry missing required 'aud:' key",
+		Severity: Error,
+		Description: "Each entry under 'id_tokens:' must be a map with an 'aud:' " +
+			"(audience) key. Without 'aud:' GitLab cannot generate the ID token " +
+			"and the job will fail.",
+		Example: `my-job:
+  id_tokens:
+    MY_TOKEN:
+      # missing aud:
+  script: vault-login.sh`,
+		Fix: `my-job:
+  id_tokens:
+    MY_TOKEN:
+      aud: https://vault.example.com
+  script: vault-login.sh`,
+	},
+
+	RuleInvalidSecret: {
+		Title:    "'secrets:' entry missing a provider key",
+		Severity: Error,
+		Description: "Each entry under 'secrets:' must specify a provider: one of " +
+			"'vault:', 'gcp_secret_manager:', or 'azure_key_vault:'. Without a " +
+			"provider GitLab cannot retrieve the secret.",
+		Example: `my-job:
+  secrets:
+    DB_PASSWORD:
+      path: secret/db/password   # no provider key
+  script: run.sh`,
+		Fix: `my-job:
+  secrets:
+    DB_PASSWORD:
+      vault:
+        engine:
+          name: kv-v2
+          path: secret
+        path: db/password
+        field: password
+  script: run.sh`,
+	},
+
+	RulePagesPublish: {
+		Title:    "'pages:' keyword publish directory missing from 'artifacts.paths'",
+		Severity: Warning,
+		Description: "A job using the 'pages:' keyword must include its publish " +
+			"directory in 'artifacts.paths'. Without this, GitLab Pages will not " +
+			"deploy the site.",
+		Example: `my-pages-job:
+  script: hugo
+  pages:
+    publish: public
+  artifacts:
+    paths:
+      - dist/   # missing public/`,
+		Fix: `my-pages-job:
+  script: hugo
+  pages:
+    publish: public
+  artifacts:
+    paths:
+      - public/`,
+	},
+
+	RuleDuplicateStage: {
+		Title:    "duplicate stage name in 'stages:'",
+		Severity: Warning,
+		Description: "A stage name appears more than once in the 'stages:' list. " +
+			"GitLab silently merges duplicate stage entries, which can make the " +
+			"pipeline order confusing.",
+		Example: `stages:
+  - build
+  - test
+  - test   # duplicate`,
+		Fix: `stages:
+  - build
+  - test`,
+	},
+
+	RuleInvalidCacheKeyFiles: {
+		Title:    "'cache.key.files' contains a glob pattern",
+		Severity: Warning,
+		Description: "'cache.key.files' must be a list of exact file paths. Glob " +
+			"patterns (*, ?, [...]) are not expanded — the literal glob string is " +
+			"used as the cache key, which probably doesn't match your intent.",
+		Example: `my-job:
+  script: npm ci
+  cache:
+    key:
+      files:
+        - package*.json   # glob — use exact path`,
+		Fix: `my-job:
+  script: npm ci
+  cache:
+    key:
+      files:
+        - package.json
+        - package-lock.json`,
+	},
+
+	RuleStaticDeadRules: {
+		Title:    "rules:if: block statically never activates",
+		Severity: Warning,
+		Description: "Every 'rules:if:' condition in this job evaluates to false " +
+			"using the variable values declared in the pipeline YAML. The job will " +
+			"never be included in any pipeline run. This check only fires when ALL " +
+			"referenced variables are declared in the YAML (predefined CI_* variables " +
+			"are not evaluated to avoid false positives).",
+		Example: `variables:
+  ENABLE_DEPLOY: "false"
+
+deploy:
+  rules:
+    - if: '$ENABLE_DEPLOY == "true"'   # always false: ENABLE_DEPLOY is "false"
+  script: ./deploy.sh`,
+		Fix: `variables:
+  ENABLE_DEPLOY: "true"   # fix the variable value
+
+deploy:
+  rules:
+    - if: '$ENABLE_DEPLOY == "true"'
+  script: ./deploy.sh
+
+# Or add an unconditional fallback:
+deploy:
+  rules:
+    - if: '$ENABLE_DEPLOY == "true"'
+    - when: manual   # allow manual trigger as a fallback
+  script: ./deploy.sh`,
+	},
+
+	RuleInheritNoDefault: {
+		Title:    "'inherit: default:' declared but no 'default:' block",
+		Severity: Warning,
+		Description: "A job declares 'inherit: default:' but the pipeline has no " +
+			"'default:' block, so the declaration has no effect. This can also fire " +
+			"when 'inherit: default: [list]' names fields that are not set in the " +
+			"'default:' block.",
+		Example: `# No default: block exists
+
+my-job:
+  inherit:
+    default: false   # no-op: nothing to opt out of
+  script: echo hi`,
+		Fix: `# Either add a default: block...
+default:
+  before_script:
+    - source venv/bin/activate
+
+my-job:
+  inherit:
+    default: false
+  script: echo hi
+
+# ...or remove the pointless inherit: declaration
+my-job:
+  script: echo hi`,
+	},
+}
diff --git a/internal/linter/if_reachability.go b/internal/linter/if_reachability.go
new file mode 100644
index 0000000..556eefa
--- /dev/null
+++ b/internal/linter/if_reachability.go
@@ -0,0 +1,104 @@
+package linter
+
+import (
+	"git.k3nny.fr/glint/internal/cicontext"
+	"git.k3nny.fr/glint/internal/model"
+)
+
+// checkRulesIfReachability (GL042): warn when every rule in a job's rules: block
+// can be statically proven to never activate given the values of variables
+// declared in the pipeline YAML. Only fires when ALL variables referenced by the
+// rules:if: expressions are declared in the pipeline or job variables: blocks —
+// predefined CI_* / GITLAB_* variables or variables not declared in YAML are
+// treated as unknown (could have any runtime value) so the check is skipped
+// conservatively to avoid false positives.
+func checkRulesIfReachability(p *model.Pipeline) []Finding {
+	if len(p.Jobs) == 0 {
+		return nil
+	}
+
+	// Collect scalar string values from pipeline-level variables.
+	pipelineVars := make(map[string]string, len(p.Variables))
+	for k, v := range p.Variables {
+		if s, ok := cicontext.ScalarString(v); ok {
+			pipelineVars[k] = s
+		}
+	}
+
+	var findings []Finding
+	for name, job := range p.Jobs {
+		if len(job.Rules) == 0 {
+			continue
+		}
+
+		// Merge pipeline vars with job-level variable overrides.
+		jobVars := make(map[string]string, len(pipelineVars)+len(job.Variables))
+		for k, v := range pipelineVars {
+			jobVars[k] = v
+		}
+		for k, v := range job.Variables {
+			if s, ok := cicontext.ScalarString(v); ok {
+				jobVars[k] = s
+			}
+		}
+
+		if f := evalRulesReachability(name, job, jobVars); f != nil {
+			findings = append(findings, *f)
+		}
+	}
+	return findings
+}
+
+// evalRulesReachability returns a GL042 finding when the job's rules: block
+// can never activate given the provided variable map, or nil if the job
+// might activate (or the check cannot be applied conservatively).
+func evalRulesReachability(name string, job model.Job, jobVars map[string]string) *Finding {
+	lookup := func(k string) string { return jobVars[k] }
+
+	for _, rule := range job.Rules {
+		// Explicit when: never — this rule is provably dead; continue.
+		if rule.When == "never" {
+			continue
+		}
+
+		// No if: condition → this rule always matches → job CAN activate.
+		if rule.If == "" {
+			return nil
+		}
+
+		// Check whether all variables referenced in the if: expression are
+		// declared in the pipeline YAML. If any are not declared (predefined
+		// CI vars, project settings, etc.), we cannot evaluate the expression
+		// and must conservatively assume the job might activate.
+		refs := extractIfVars(rule.If)
+		allDeclared := true
+		for _, ref := range refs {
+			if _, ok := jobVars[ref]; !ok {
+				// Variable not in YAML (predefined or unknown) → cannot evaluate.
+				allDeclared = false
+				break
+			}
+		}
+		if !allDeclared {
+			return nil // conservative: job might activate
+		}
+
+		// All referenced variables are declared; evaluate the expression.
+		// Use strict mode (unparse → false) to avoid matching unparseable expressions.
+		if cicontext.EvalIfStrict(rule.If, lookup) {
+			// This rule's condition evaluates to true → job CAN activate.
+			return nil
+		}
+		// Expression evaluated to false → this rule cannot activate; continue.
+	}
+
+	// No rule could activate the job.
+	return &Finding{
+		Severity: Warning,
+		Rule:     RuleStaticDeadRules,
+		Job:      name,
+		File:     job.File,
+		Line:     job.Line,
+		Message:  "rules: block can never activate: all if: conditions evaluate to false given the declared pipeline variables",
+	}
+}
diff --git a/internal/linter/if_reachability_test.go b/internal/linter/if_reachability_test.go
new file mode 100644
index 0000000..7fe0516
--- /dev/null
+++ b/internal/linter/if_reachability_test.go
@@ -0,0 +1,152 @@
+package linter
+
+import (
+	"testing"
+
+	"git.k3nny.fr/glint/internal/model"
+)
+
+func TestCheckRulesIfReachability(t *testing.T) {
+	makeJob := func(vars map[string]any, rules []model.Rule) model.Job {
+		return model.Job{Variables: vars, Rules: rules}
+	}
+
+	cases := []struct {
+		name        string
+		pipelineVars map[string]any
+		jobs        map[string]model.Job
+		wantHit     []string // job names that should produce GL042
+		wantMiss    []string // job names that should NOT produce GL042
+	}{
+		{
+			name:         "declared var always false — GL042 fires",
+			pipelineVars: map[string]any{"DEPLOY": "false"},
+			jobs: map[string]model.Job{
+				"deploy": makeJob(nil, []model.Rule{
+					{If: `$DEPLOY == "true"`, When: "on_success"},
+				}),
+			},
+			wantHit:  []string{"deploy"},
+			wantMiss: nil,
+		},
+		{
+			name:         "declared var matches — no finding",
+			pipelineVars: map[string]any{"DEPLOY": "true"},
+			jobs: map[string]model.Job{
+				"deploy": makeJob(nil, []model.Rule{
+					{If: `$DEPLOY == "true"`, When: "on_success"},
+				}),
+			},
+			wantHit:  nil,
+			wantMiss: []string{"deploy"},
+		},
+		{
+			name:         "predefined CI_ var — skip check conservatively",
+			pipelineVars: nil,
+			jobs: map[string]model.Job{
+				"branch-job": makeJob(nil, []model.Rule{
+					{If: `$CI_COMMIT_BRANCH == "never-exists"`, When: "on_success"},
+				}),
+			},
+			wantHit:  nil,
+			wantMiss: []string{"branch-job"},
+		},
+		{
+			name:         "undeclared var — skip check conservatively",
+			pipelineVars: nil,
+			jobs: map[string]model.Job{
+				"my-job": makeJob(nil, []model.Rule{
+					{If: `$UNKNOWN_VAR == "x"`, When: "on_success"},
+				}),
+			},
+			wantHit:  nil,
+			wantMiss: []string{"my-job"},
+		},
+		{
+			name:         "unconditional rule — job can always activate",
+			pipelineVars: map[string]any{"DEPLOY": "false"},
+			jobs: map[string]model.Job{
+				"my-job": makeJob(nil, []model.Rule{
+					{If: `$DEPLOY == "true"`, When: "never"},
+					{When: "on_success"},
+				}),
+			},
+			wantHit:  nil,
+			wantMiss: []string{"my-job"},
+		},
+		{
+			name:         "all rules when:never — GL042 fires (not GL033 territory overlap)",
+			pipelineVars: map[string]any{"DEPLOY": "false"},
+			jobs: map[string]model.Job{
+				"my-job": makeJob(nil, []model.Rule{
+					{If: `$DEPLOY == "true"`, When: "on_success"},
+					{When: "never"},
+				}),
+			},
+			// Rule 1 evaluates to false; Rule 2 is explicit never → all dead.
+			wantHit:  []string{"my-job"},
+			wantMiss: nil,
+		},
+		{
+			name:         "job-level var overrides pipeline var",
+			pipelineVars: map[string]any{"FLAG": "false"},
+			jobs: map[string]model.Job{
+				"my-job": makeJob(map[string]any{"FLAG": "true"}, []model.Rule{
+					{If: `$FLAG == "true"`, When: "on_success"},
+				}),
+			},
+			// Job-level FLAG="true" makes the if: evaluate to true → no finding.
+			wantHit:  nil,
+			wantMiss: []string{"my-job"},
+		},
+		{
+			name:         "no rules — nothing to check",
+			pipelineVars: map[string]any{"DEPLOY": "false"},
+			jobs: map[string]model.Job{
+				"my-job": makeJob(nil, nil),
+			},
+			wantHit:  nil,
+			wantMiss: []string{"my-job"},
+		},
+		{
+			name:         "boolean variable evaluates correctly",
+			pipelineVars: map[string]any{"FLAG": false}, // bool false
+			jobs: map[string]model.Job{
+				"my-job": makeJob(nil, []model.Rule{
+					{If: `$FLAG == "true"`, When: "on_success"},
+				}),
+			},
+			// ScalarString(false) → "false"; "false" == "true" → false → GL042 fires.
+			wantHit:  []string{"my-job"},
+			wantMiss: nil,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			p := &model.Pipeline{
+				Variables: tc.pipelineVars,
+				Jobs:      tc.jobs,
+			}
+			findings := checkRulesIfReachability(p)
+
+			hitSet := make(map[string]bool)
+			for _, f := range findings {
+				if f.Rule == RuleStaticDeadRules {
+					hitSet[f.Job] = true
+				}
+			}
+
+			for _, want := range tc.wantHit {
+				if !hitSet[want] {
+					t.Errorf("expected GL042 for job %q but it was not reported; findings: %v", want, findings)
+				}
+			}
+			for _, notWant := range tc.wantMiss {
+				if hitSet[notWant] {
+					t.Errorf("unexpected GL042 for job %q", notWant)
+				}
+			}
+		})
+	}
+}
diff --git a/internal/linter/inherit_completeness.go b/internal/linter/inherit_completeness.go
new file mode 100644
index 0000000..9cb72dd
--- /dev/null
+++ b/internal/linter/inherit_completeness.go
@@ -0,0 +1,112 @@
+package linter
+
+import (
+	"fmt"
+	"strings"
+
+	"git.k3nny.fr/glint/internal/model"
+)
+
+// checkInheritCompleteness (GL043): warn when a job's 'inherit: default:'
+// declaration is dead — either because there is no 'default:' block in the
+// pipeline, or because the list form references fields that are not defined
+// in the 'default:' block.
+func checkInheritCompleteness(p *model.Pipeline) []Finding {
+	var findings []Finding
+	for name, job := range p.Jobs {
+		findings = append(findings, checkJobInheritCompleteness(p, name, job)...)
+	}
+	return findings
+}
+
+func checkJobInheritCompleteness(p *model.Pipeline, name string, job model.Job) []Finding {
+	if job.Inherit == nil {
+		return nil
+	}
+	m, ok := job.Inherit.(map[string]any)
+	if !ok {
+		return nil
+	}
+	defaultVal, hasDefault := m["default"]
+	if !hasDefault {
+		return nil
+	}
+
+	// Case 1: no default: block at all — the entire declaration is a no-op.
+	if p.Default == nil {
+		return []Finding{{
+			Severity: Warning,
+			Rule:     RuleInheritNoDefault,
+			Job:      name,
+			File:     job.File,
+			Line:     job.Line,
+			Message:  "'inherit: default:' is declared but the pipeline has no 'default:' block — declaration has no effect",
+		}}
+	}
+
+	// Case 2: list form — check for field names not set in default:.
+	list, ok := defaultVal.([]any)
+	if !ok {
+		// bool form (true/false) with a non-nil default: block is always valid.
+		return nil
+	}
+
+	var dead []string
+	for _, item := range list {
+		field, ok := item.(string)
+		if !ok {
+			continue
+		}
+		if !defaultBlockHasField(p.Default, field) {
+			dead = append(dead, field)
+		}
+	}
+	if len(dead) == 0 {
+		return nil
+	}
+	return []Finding{{
+		Severity: Warning,
+		Rule:     RuleInheritNoDefault,
+		Job:      name,
+		File:     job.File,
+		Line:     job.Line,
+		Message: fmt.Sprintf(
+			"'inherit: default: [%s]': %s not defined in the 'default:' block — %s",
+			strings.Join(dead, ", "),
+			pluralIs(len(dead)),
+			"these entries have no effect",
+		),
+	}}
+}
+
+// defaultBlockHasField reports whether the given field name has a non-zero value
+// in the default: block. Unknown field names return true (conservative).
+func defaultBlockHasField(d *model.DefaultConfig, field string) bool {
+	switch field {
+	case "image":
+		return d.Image != nil
+	case "before_script":
+		return d.BeforeScript != nil
+	case "after_script":
+		return d.AfterScript != nil
+	case "cache":
+		return d.Cache != nil
+	case "artifacts":
+		return d.Artifacts != nil
+	case "retry":
+		return d.Retry != nil
+	case "timeout":
+		return d.Timeout != ""
+	case "tags":
+		return len(d.Tags) > 0
+	}
+	// Unknown field name — conservatively assume it might be defined.
+	return true
+}
+
+func pluralIs(n int) string {
+	if n == 1 {
+		return "this field is"
+	}
+	return "these fields are"
+}
diff --git a/internal/linter/inherit_completeness_test.go b/internal/linter/inherit_completeness_test.go
new file mode 100644
index 0000000..020dfbd
--- /dev/null
+++ b/internal/linter/inherit_completeness_test.go
@@ -0,0 +1,94 @@
+package linter
+
+import (
+	"testing"
+
+	"git.k3nny.fr/glint/internal/model"
+)
+
+func TestCheckInheritCompleteness(t *testing.T) {
+	cases := []struct {
+		name    string
+		default_ *model.DefaultConfig
+		inherit any // job.Inherit value
+		wantHit bool
+	}{
+		{
+			name:    "no inherit — no finding",
+			inherit: nil,
+			wantHit: false,
+		},
+		{
+			name:    "inherit: default: false, no default block — GL043",
+			inherit: map[string]any{"default": false},
+			wantHit: true,
+		},
+		{
+			name:    "inherit: default: true, no default block — GL043",
+			inherit: map[string]any{"default": true},
+			wantHit: true,
+		},
+		{
+			name:    "inherit: default: [image], no default block — GL043",
+			inherit: map[string]any{"default": []any{"image"}},
+			wantHit: true,
+		},
+		{
+			name:     "inherit: default: false, default block exists — no finding",
+			default_: &model.DefaultConfig{Image: "node:20"},
+			inherit:  map[string]any{"default": false},
+			wantHit:  false,
+		},
+		{
+			name:     "inherit: default: [image], image in default — no finding",
+			default_: &model.DefaultConfig{Image: "node:20"},
+			inherit:  map[string]any{"default": []any{"image"}},
+			wantHit:  false,
+		},
+		{
+			name:     "inherit: default: [before_script], before_script NOT in default — GL043",
+			default_: &model.DefaultConfig{Image: "node:20"},
+			inherit:  map[string]any{"default": []any{"before_script"}},
+			wantHit:  true,
+		},
+		{
+			name:     "inherit: default: [image, before_script], only image in default — GL043 for before_script",
+			default_: &model.DefaultConfig{Image: "node:20"},
+			inherit:  map[string]any{"default": []any{"image", "before_script"}},
+			wantHit:  true,
+		},
+		{
+			name:     "inherit: variables only — no default check",
+			default_: nil,
+			inherit:  map[string]any{"variables": false},
+			wantHit:  false,
+		},
+		{
+			name:     "inherit: unknown field in list — conservative, no finding",
+			default_: &model.DefaultConfig{Image: "node:20"},
+			inherit:  map[string]any{"default": []any{"nonexistent_field"}},
+			wantHit:  false, // unknown fields return true from defaultBlockHasField
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			job := model.Job{Inherit: tc.inherit}
+			p := &model.Pipeline{
+				Default: tc.default_,
+				Jobs:    map[string]model.Job{"test-job": job},
+			}
+			findings := checkInheritCompleteness(p)
+
+			hit := false
+			for _, f := range findings {
+				if f.Rule == RuleInheritNoDefault {
+					hit = true
+				}
+			}
+			if hit != tc.wantHit {
+				t.Errorf("GL043 hit=%v, want=%v; findings: %v", hit, tc.wantHit, findings)
+			}
+		})
+	}
+}
diff --git a/internal/linter/linter.go b/internal/linter/linter.go
index 53268d7..b1aa2a2 100644
--- a/internal/linter/linter.go
+++ b/internal/linter/linter.go
@@ -62,6 +62,8 @@ func Lint(p *model.Pipeline) []Finding {
 	findings = append(findings, checkNeeds(p)...)
 	findings = append(findings, checkDependencies(p)...)
 	findings = append(findings, checkVariableRefs(p)...)
+	findings = append(findings, checkRulesIfReachability(p)...)
+	findings = append(findings, checkInheritCompleteness(p)...)
 	slices.SortStableFunc(findings, func(a, b Finding) int {
 		if c := cmp.Compare(a.File, b.File); c != 0 {
 			return c
diff --git a/internal/linter/rules.go b/internal/linter/rules.go
index c7816b9..c43eaaa 100644
--- a/internal/linter/rules.go
+++ b/internal/linter/rules.go
@@ -143,4 +143,15 @@ const (
 
 	// GL041: cache.key.files contains a glob pattern; it must be a list of exact file paths.
 	RuleInvalidCacheKeyFiles = "GL041"
+
+	// GL042: every rules:if: condition in a job's rules: block evaluates to false
+	// given the values of variables declared in the pipeline YAML, so the job can
+	// never be active. Only fires when all referenced variables are declared
+	// (predefined CI_* / GITLAB_* vars are not evaluated to avoid false positives).
+	RuleStaticDeadRules = "GL042"
+
+	// GL043: a job declares 'inherit: default:' (true, false, or list) but the
+	// pipeline has no 'default:' block, making the declaration a no-op. Also fires
+	// when 'inherit: default: [list]' names fields not set in the default: block.
+	RuleInheritNoDefault = "GL043"
 )
diff --git a/testdata/inherit_dead.yml b/testdata/inherit_dead.yml
new file mode 100644
index 0000000..e54c20f
--- /dev/null
+++ b/testdata/inherit_dead.yml
@@ -0,0 +1,26 @@
+stages:
+  - build
+  - test
+
+# No default: block — any inherit: default: declaration is a no-op.
+
+# GL043: inherit: default: false but no default: block.
+isolated-job:
+  stage: build
+  inherit:
+    default: false
+  script: echo isolated
+
+# GL043: inherit: default: [list] but no default: block.
+selective-inherit-job:
+  stage: test
+  inherit:
+    default: [image, tags]
+  script: echo selective
+
+# Not GL043: inherit only touches variables: (no default: check needed).
+vars-inherit-job:
+  stage: test
+  inherit:
+    variables: false
+  script: echo vars-only
diff --git a/testdata/inherit_dead_fields.yml b/testdata/inherit_dead_fields.yml
new file mode 100644
index 0000000..bf41d73
--- /dev/null
+++ b/testdata/inherit_dead_fields.yml
@@ -0,0 +1,20 @@
+stages:
+  - build
+  - test
+
+default:
+  image: node:20
+
+# GL043: before_script is in the list but not defined in default:.
+selective-bad:
+  stage: build
+  inherit:
+    default: [image, before_script]   # before_script not in default:
+  script: echo hi
+
+# Not GL043: image IS defined in default: — list is valid.
+selective-good:
+  stage: test
+  inherit:
+    default: [image]
+  script: echo hi
diff --git a/testdata/keywords_valid.yml b/testdata/keywords_valid.yml
index 9de6f72..8e98f96 100644
--- a/testdata/keywords_valid.yml
+++ b/testdata/keywords_valid.yml
@@ -9,6 +9,10 @@ workflow:
       when: always
     - when: never
 
+default:
+  tags:
+    - docker
+
 variables:
   GO_VERSION: "1.26"
 
diff --git a/testdata/static_dead_rules.yml b/testdata/static_dead_rules.yml
new file mode 100644
index 0000000..9b78f0b
--- /dev/null
+++ b/testdata/static_dead_rules.yml
@@ -0,0 +1,48 @@
+stages:
+  - deploy
+  - test
+
+variables:
+  DEPLOY: "false"
+  SKIP_TEST: "true"
+
+# GL042: both if: conditions always evaluate to false given the declared variables.
+always-dead-deploy:
+  stage: deploy
+  rules:
+    - if: '$DEPLOY == "true"'
+      when: on_success
+  script: echo deploy
+
+# GL042: if: is false, explicit when:on_success rule — still never fires.
+always-dead-test:
+  stage: test
+  rules:
+    - if: '$SKIP_TEST == "false"'
+      when: on_success
+  script: echo test
+
+# Not GL042: references a predefined CI_ variable → unknown value → skip check.
+predefined-var-job:
+  stage: test
+  rules:
+    - if: '$CI_COMMIT_BRANCH == "nonexistent-branch"'
+      when: on_success
+  script: echo branch
+
+# Not GL042: has an unconditional rule (no if: → always matches).
+unconditional-job:
+  stage: test
+  rules:
+    - if: '$DEPLOY == "true"'
+      when: never
+    - when: on_success
+  script: echo always
+
+# Not GL042: references undeclared variable → unknown → conservative.
+undeclared-var-job:
+  stage: test
+  rules:
+    - if: '$UNDECLARED_VAR == "something"'
+      when: on_success
+  script: echo undeclared