gitlab-sim

Disclaimer: This tool was built through iterative AI-assisted development with Claude. 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.

A local tool to validate and lint .gitlab-ci.yml pipelines without needing a GitLab server.

Features

• YAML validation — detects malformed pipeline files early
• Stage validation — every job's stage must be declared in stages
• extends: resolution — resolves single and multi-level template inheritance before linting, so derived jobs are evaluated against their fully merged definition
• needs: DAG validation — checks that needs: references exist, respect stage ordering, and contain no circular dependencies
• dependencies: validation — checks that artifact dependency references exist and are in earlier stages
• Keyword validation — validates constraints on when, parallel, retry, allow_failure, trigger, artifacts, cache, release, environment, coverage, rules, and more
• Remote project includes — fetches include: project: templates from the GitLab API so extends/needs can be validated against the full merged pipeline
• CI/CD catalog components — resolves include: component: references from the GitLab CI/CD Catalog; public components work without a token
• Deprecation warnings — flags only/except usage in favour of rules
• Graph output — emits Mermaid diagrams for the include dependency tree and the pipeline jobs layout (DAG or classic stage ordering)
• Context simulation — pass --branch, --tag, or --source to see which jobs would be active, manual, or skipped for a specific branch push, tag, or pipeline event; evaluates rules:if: expressions and only/except filters

Requirements

• Go 1.21 or later
• Task (optional, for development tasks)

Installation

git clone https://git.k3nny.fr/gitlab-sim
cd gitlab-sim
go build -o gitlab-sim ./cmd/gitlab-sim/...

Or with Task:

task build

Usage

gitlab-sim [options] <pipeline.yml>

Exits 0 when no errors are found, 1 when at least one error is reported.

Remote project includes

Pipelines that include templates from other GitLab projects are supported. Provide a token so gitlab-sim can fetch them:

# personal access token (read_api scope)
GITLAB_TOKEN=glpat-xxxx gitlab-sim .gitlab-ci.yml

# CI/CD job token (when running inside a pipeline)
CI_JOB_TOKEN=$CI_JOB_TOKEN gitlab-sim .gitlab-ci.yml

# self-hosted GitLab
GITLAB_TOKEN=glpat-xxxx GITLAB_URL=https://gitlab.example.com gitlab-sim .gitlab-ci.yml

# or via flags
gitlab-sim --token glpat-xxxx --gitlab-url https://gitlab.example.com .gitlab-ci.yml

Project includes require a token; without one they are skipped with a warning and the rest of the pipeline is linted as-is.

Component includes (include: component: ...) attempt the fetch unauthenticated, so public CI/CD Catalog components work without a token. A warning is emitted if the fetch fails.

Token resolution order (first non-empty wins):

Source	Header used
--token flag / GITLAB_TOKEN	PRIVATE-TOKEN
CI_JOB_TOKEN	JOB-TOKEN
GITLAB_PRIVATE_TOKEN	PRIVATE-TOKEN

Instance URL resolution order: --gitlab-url flag → CI_SERVER_URL → GITLAB_URL → https://gitlab.com

Component reference format

<host>/<project-path>/<component-name>@<version>

gitlab.com/components/secret-detection/secret-detection@v0.1.0
gitlab.com/my-org/ci-catalog/lint@main
gitlab.example.com/platform/components/build@~latest

The component file is looked up in order:

1. templates/<component-name>.yml (single-file layout)
2. templates/<component-name>/template.yml (directory layout)

Component input parameters (with:) are not validated — they are resolved by GitLab at runtime. Jobs in fetched components may use $[[ inputs.xxx ]] placeholders in fields like stage; gitlab-sim skips those fields rather than producing false positive errors.

Graph output

Pass --graph to visualise the pipeline instead of running lint rules.

# Include dependency graph (which files include which) → Mermaid to stdout
gitlab-sim --graph includes .gitlab-ci.yml > includes.mmd

# GitLab-like pipeline layout → PNG (or SVG fallback) written to --graph-out dir
gitlab-sim --graph pipeline .gitlab-ci.yml
# prints the output file path, e.g.: gitlab-sim-out/pipeline-20260607-143022.png

# Both at once: Mermaid to stdout + pipeline file path to stderr
gitlab-sim --graph all .gitlab-ci.yml > includes.mmd

# Custom output directory
gitlab-sim --graph pipeline --graph-out /tmp/graphs .gitlab-ci.yml

Include graph (--graph includes) — Mermaid flowchart written to stdout. Pipe to a .mmd file or paste into mermaid.live. One node per include entry, colour-coded by type:

• Orange (bold): the main pipeline file
• Purple: project: includes
• Green: component: includes
• Blue: local: includes
• Grey: remote: URL includes
• Light orange: GitLab-provided template: includes

Pipeline graph (--graph pipeline) — GitLab CI-style SVG rendered to a timestamped file in the --graph-out directory (default: gitlab-sim-out/). Converted to PNG automatically when rsvg-convert, inkscape, or magick is available; falls back to SVG otherwise. Jobs are colour-coded by type:

• Blue (#1f75cb): regular jobs
• Orange (#fc6d26): when: manual jobs
• Purple (#6b4fbb): trigger: jobs
• Amber (#fca326): when: delayed jobs

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.

Context simulation

Pass --branch, --tag, or --source to see which jobs would run for a given pipeline event. The pipeline is still fully linted; context output is printed first.

# What runs on a push to develop?
gitlab-sim --branch develop .gitlab-ci.yml

# What runs when a v1.2.0 tag is pushed?
gitlab-sim --tag v1.2.0 .gitlab-ci.yml

# Merge request pipeline
gitlab-sim --source merge_request_event .gitlab-ci.yml

# Arbitrary variable overrides (repeatable)
gitlab-sim --branch main --var DEPLOY_ENV=production .gitlab-ci.yml

Evaluated:

• rules:if: — full expression language: ==, !=, =~, !~, &&, ||, !, (), $VAR, string literals, null
• only: / except: — ref keywords (branches, tags, merge_requests, schedules, …), branch name globs (feat/*), and /regex/ patterns

Not evaluated (no git tree at lint time): rules:changes:, rules:exists:. Rules without an if: clause always match.

Predefined variables set automatically by the shortcut flags:

Flag	Variables populated
--branch <name>	CI_COMMIT_BRANCH, CI_COMMIT_REF_NAME, CI_COMMIT_REF_SLUG, CI_PIPELINE_SOURCE=push
--tag <name>	CI_COMMIT_TAG, CI_COMMIT_REF_NAME, CI_COMMIT_REF_SLUG, CI_PIPELINE_SOURCE=push (clears CI_COMMIT_BRANCH)
--source <event>	CI_PIPELINE_SOURCE
--var KEY=VALUE	any variable; overrides shortcuts

Example output

# Clean pipeline, no context
OK: .gitlab-ci.yml — no issues found (5 jobs, 3 stages)

# With --branch develop context
Context: branch=develop, source=push

Active  (3): build, deploy-staging, test
Skipped (2): deploy-prod, release-notes

OK: .gitlab-ci.yml — no issues found (5 jobs, 3 stages)

# With --tag v1.0.0 context
Context: tag=v1.0.0, source=push

Active  (4): build, deploy-prod, release-notes, test
Skipped (1): deploy-staging

OK: .gitlab-ci.yml — no issues found (5 jobs, 3 stages)

# Pipeline with issues
[ERROR] job "deploy": stage "production" is not defined in 'stages'
[ERROR] job "test": needs unknown job "build-app"
[WARNING] job "old-job": 'only'/'except' are deprecated; prefer 'rules'

3 finding(s): 2 error(s)

Lint rules

Pipeline-level

Severity	Rule
ERROR	workflow.rules[*].when is not always or never
WARNING	No stages defined (GitLab falls back to default stages)

Job-level — structure

Severity	Rule
ERROR	Job is missing required script (or run) — non-trigger, non-template jobs
ERROR	Job references a stage not declared in stages
ERROR	only and rules used together on the same job
ERROR	except and rules used together on the same job
WARNING	only/except used (deprecated, prefer rules)

Job-level — keyword constraints

Severity	Rule
ERROR	when is not one of on_success, on_failure, always, manual, delayed, never
ERROR	when: delayed without start_in
ERROR	start_in set but when is not delayed
ERROR	parallel integer not in range 2–200
ERROR	parallel map form missing matrix key
ERROR	retry integer not in range 0–2
ERROR	retry.max not in range 0–2
ERROR	retry.when contains an invalid failure type
ERROR	allow_failure is not a boolean or a map with exit_codes
ERROR	interruptible is not a boolean
ERROR	trigger job also has script
ERROR	trigger map missing project or include
ERROR	coverage is not a regex pattern wrapped in /
ERROR	release missing required tag_name
ERROR	environment.url set without environment.name
ERROR	environment.action is not one of start, stop, prepare, verify, access
ERROR	artifacts.when is not on_success, on_failure, or always
ERROR	artifacts.expose_as set without artifacts.paths
ERROR	cache.when is not on_success, on_failure, or always
ERROR	cache.policy is not pull, push, or pull-push
ERROR	rules[*].when is not one of the valid when values
ERROR	image map form missing name key
ERROR	inherit.default / inherit.variables is not a boolean or list
WARNING	pages job artifacts.paths does not include public

Cross-job graph

Severity	Rule
ERROR	needs: references a job that does not exist
ERROR	needs: references a job in a later stage
ERROR	Circular dependency detected in needs: graph
ERROR	dependencies: references a job that does not exist
ERROR	dependencies: references a job in the same or a later stage
ERROR	extends: references an unknown job
ERROR	Cycle detected in extends: graph

Hidden jobs (templates)

Jobs whose name starts with . are treated as reusable templates and skipped for most rules. This matches GitLab's own behaviour.

Development

This project uses Task as a task runner.

task              # list available tasks
task build        # compile the binary
task test         # run Go unit tests
task lint-go      # run go vet
task validate     # run the binary against all testdata fixtures
task ci           # full check: vet → test → build → validate
task clean        # remove build artifacts

Project structure

.
├── cmd/gitlab-sim/     # CLI entrypoint
├── internal/
│   ├── cicontext/      # CI variable context, rules:if: evaluator, job reachability
│   ├── fetcher/        # GitLab API client (project include fetching)
│   ├── graph/          # Mermaid and SVG/PNG graph generators
│   ├── linter/         # lint rules and findings
│   ├── model/          # pipeline data structures and YAML parser
│   └── resolver/       # extends: resolution and project include merging
├── testdata/           # sample pipelines used for manual validation
├── Taskfile.yml
└── go.mod