actionlint is a static checker for GitHub Actions workflow files. Try it online!

Features:

• Syntax check for workflow files to check unexpected or missing keys following workflow syntax
• Strong type check for ${{ }} expressions to catch several semantic errors like access to not existing property, type mismatches, ...
• shellcheck and pyflakes integrations for scripts in run:
• Other several useful checks; glob syntax validation, dependencies check for needs:, runner label validation, cron syntax validation, ...

See 'Checks' section for full list of checks done by actionlint.

Example of broken workflow:

on:
  push:
    branch: main
    tags:
      - 'v\d+'
jobs:
  test:
    strategy:
      matrix:
        os: [macos-latest, linux-latest]
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/checkout@v2
      - uses: actions/cache@v2
        with:
          path: ~/.npm
          key: ${{ matrix.platform }}-node-${{ hashFiles('**/package-lock.json') }}
        if: ${{ github.repository.permissions.admin == true }}
      - run: npm install && npm test

Output from actionlint:

Basically all you need to do is running acitonlint command in your repository. actionlint automatically detects workflows in your repository and reports errors in them. actionlint focuses on finding out mistakes. It tries to catch errors as much as possible and make false positives as minimal as possible.

• Running workflow is time consuming. You need to push the changes and wait until the workflow runs on GitHub even if it contains some trivial mistakes. act is useful to run the workflow locally. But it is not suitable for CI and still time consuming when your workflow gets larger.
• Checks of workflow files by GitHub are very loose. It reports no error even if unexpected keys are in mappings (meant that some typos in keys). And also it reports no error when accessing to property which is actually not existing. For example matrix.foo when no foo is defined in matrix: section, it is evaluated to null and causes no error.
• Some mistakes silently break a workflow. Most common case I saw is specifying missing property to cache key. In the case cache silently does not work properly but workflow itself runs without error. So you might not notice the mistake forever.

Tap this repository and install actionlint package.

brew tap "rhysd/actionlint" "https://github.com/rhysd/actionlint"
brew install actionlint

Download an archive file from releases page for your platform, unarchive it and put the executable file to a directory in $PATH.

Prebuilt binaries are built at each release by CI for the following OS and arch:

• macOS (x86_64, arm64)
• Linux (i386, x86_64, arm32, arm64)
• Windows (i386, x86_64)
• FreeBSD (i386, x86_64)

Note: The author doesn't have Apple M1 environment so darwin/arm64 target binary is not tested.

Please try the download script. It downloads the latest version of actionlint (actionlint.exe on Windows and actionlint on other OSes) to the current directory automatically. On GitHub Actions environment, it sets a file path of downloaded executable to executable output in order to use the executable in the following steps easily.

Here is an example of simple workflow to run actionlint on GitHub Actions. Please ensure shell: bash since the default shell for Windows runners is pwsh.

name: Lint GitHub Actions workflows
on: [push, pull_request]

jobs:
  actionlint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Download actionlint
        id: get_actionlint
        run: bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
        shell: bash
      - name: Check workflow files
        run: ${{ steps.get_actionlint.outputs.executable }} -color
        shell: bash

or simply run

- name: Check workflow files
  run: |
    bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
    ./actionlint -color
  shell: bash

If you want to enable shellcheck integration, install shellcheck command as follows:

- name: Install shellcheck to enable shellcheck integration
  run: sudo apt install shellcheck

Go toolchain is necessary.

# Install the latest stable version
go install github.com/rhysd/actionlint/cmd/actionlint@latest

# Install the head of main branch
go install github.com/rhysd/actionlint/cmd/actionlint

Thanks to WebAssembly, actionlint playground is available on your browser. It never sends any data to outside of your browser.

https://rhysd.github.io/actionlint/

Paste your workflow content to the code editor at left pane. It automatically shows the results at right pane. When editing the workflow content in the code editor, the results will be updated on the fly. Clicking an error message in the results table moves a cursor to position of the error in the code editor.

With no argument, actionlint finds all workflow files in the current repository and checks them.

actionlint

When paths to YAML workflow files are given as arguments, actionlint checks them.

actionlint path/to/workflow1.yaml path/to/workflow2.yaml

See actionlint -h for all flags and options.

This section describes all checks done by actionlint with example input and output.

List of checks:

• Unexpected keys
• Missing required keys or key duplicates
• Unexpected empty mappings
• Unexpected mapping values
• Syntax check for expression ${{ }}
• Type checks for expression syntax in ${{ }}
• Contexts and built-in functions
• Contextual typing for steps.<step_id> objects
• Contextual typing for matrix object
• Contextual typing for needs object
• shellcheck integration for run:
• pyflakes integration for run:
• Job dependencies validation
• Matrix values
• Webhook events validation
• Glob filter pattern syntax validation
• CRON syntax check at schedule:
• Runner labels
• Action format in uses:
• Local action inputs validation at with:
• Shell name validation at shell:
• Job ID and step ID uniqueness
• Hardcoded credentials
• Environment variable names

Note that actionlint focuses on catching mistakes in workflow files. If you want some general code style checks, please consider to use a general YAML checker like yamllint.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    step:

Output:

test.yaml:5:5: unexpected key "step" for "job" section. expected one of "name", "needs", "runs-on", "permissions", "environment", "concurrency", "outputs", "env", "defaults", "if", "steps", "timeout-minutes", "strategy", "continue-on-error", "container", "services" [syntax-check]
  |
5 |     step:
  |     ^~~~~

Playground

Workflow syntax defines what keys can be defined in which mapping object. When other keys are defined, they are simply ignored and don't affect workflow behavior. It means typo in keys is not detected by GitHub.

actionlint can detect unexpected keys while parsing workflow syntax and report them as error.

Example input:

on: push
jobs:
  test:
    steps:
      - run: echo 'hello'
  TEST:
    runs-on: ubuntu-latest
    steps:
      - run: echo 'bye'

Output:

test.yaml:6:3: key "test" is duplicate in "jobs" section. previously defined at line:3,col:3. note that key names are case insensitive [syntax-check]
  |
6 |   TEST:
  |   ^~~~~
test.yaml:4:5: "runs-on" section is missing in job "test" [syntax-check]
  |
4 |     steps:
  |     ^~~~~~

Playground

Some mappings must include specific keys. For example, job mapping must include runs-on: and steps:.

And duplicate in keys is not allowed. In workflow syntax, comparing keys is case insensitive. For example, job ID test in lower case and job ID TEST in upper case are not able to exist in the same workflow.

actionlint checks these missing required keys and duplicate of keys while parsing, and reports an error.

Example input:

on: push
jobs:

Output:

test.yaml:2:6: "jobs" section should not be empty. please remove this section if it's unnecessary [syntax-check]
  |
2 | jobs:
  |      ^

Playground

Some mappings and sequences should not be empty. For example, steps: must include at least one step.

actionlint checks such mappings and sequences are not empty while parsing, and reports the empty mappings and sequences as error.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    permissions:
      issues: foo
    continue-on-error: foo
    steps:
      - run: echo 'hello'

Output:

test.yaml:6:15: permission must be one of "none", "read", "write" but got "foo" [syntax-check]
  |
6 |       issues: foo
  |               ^~~
test.yaml:7:24: expecting a string with ${{...}} expression or boolean literal "true" or "false", but found plain text node [syntax-check]
  |
7 |     continue-on-error: foo
  |                        ^~~

Playground

Some mapping's values are restricted to some constant strings. For example, values of permissions: mappings should be one of none, read, write. And several mapping values expect boolean value like true or false.

actionlint checks such constant strings are used properly while parsing, and reports an error when unexpected string value is specified.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      # " is not available for string literal delimiter
      - run: echo '${{ "hello" }}'
      # + operator does not exist
      - run: echo '${{ 1 + 1 }}'
      # Missing ')' paren
      - run: echo "${{ toJson(hashFiles('**/lock', '**/cache/') }}"
      # unexpected end of input
      - run: echo '${{ github.event. }}'

Output:

test.yaml:7:25: got unexpected character '"' while lexing expression, expecting '_', '\'', '}', '(', ')', '[', ']', '.', '!', '<', '>', '=', '&', ... [expression]
  |
7 |       - run: echo '${{ "hello" }}'
  |                         ^~~~~~
test.yaml:9:27: got unexpected character '+' while lexing expression, expecting '_', '\'', '}', '(', ')', '[', ']', '.', '!', '<', '>', '=', '&', ... [expression]
  |
9 |       - run: echo '${{ 1 + 1 }}'
  |                           ^
test.yaml:11:65: unexpected end of input while parsing arguments of function call. expecting ",", ")" [expression]
   |
11 |       - run: echo "${{ toJson(hashFiles('**/lock', '**/cache/') }}"
   |                                                                 ^~~
test.yaml:13:38: unexpected end of input while parsing object property dereference like 'a.b' or array element dereference like 'a.*'. expecting "IDENT", "*" [expression]
   |
13 |       - run: echo '${{ github.event. }}'
   |                                      ^~~

Playground

actionlint lexes and parses expression in ${{ }} following the expression syntax document. It can detect many syntax errors like invalid characters, missing parens, unexpected end of input, ...

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      # Basic type error like index access to object
      - run: echo '${{ env[0] }}'
      # Properties in objects are strongly typed. So missing property can be caught
      - run: echo '${{ job.container.os }}'
      # github.repository is string. So accessing .owner is invalid
      - run: echo '${{ github.repository.owner }}'

Output:

test.yaml:7:28: property access of object must be type of string but got "number" [expression]
  |
7 |       - run: echo '${{ env[0] }}'
  |                            ^~
test.yaml:9:24: property "os" is not defined in object type {id: string; network: string} [expression]
  |
9 |       - run: echo '${{ job.container.os }}'
  |                        ^~~~~~~~~~~~~~~~
test.yaml:11:24: receiver of object dereference "owner" must be type of object but got "string" [expression]
   |
11 |       - run: echo '${{ github.repository.owner }}'
   |                        ^~~~~~~~~~~~~~~~~~~~~~~

Playground

Type checks for expression syntax in ${{ }} are done by semantics checker. Note that actual type checks by GitHub Actions runtime is loose. For example any object value can be assigned into string value as string "Object". But such loose conversions are bugs in almost all cases. actionlint checks types more strictly.

There are two types of object types internally. One is an object which is strict for properties, which causes a type error when trying to access to unknown properties. And another is an object which is not strict for properties, which allows to access to unknown properties. In the case, accessing to unknown property is typed as any.

When the type check cannot be done statically, the type is deduced to any (e.g. return type from toJSON()).

And ${{ }} can be used for expanding values.

Example input:

on: push
jobs:
  test:
    strategy:
      matrix:
        env_string:
          - 'FOO=BAR'
          - 'FOO=PIYO'
        env_object:
          - FOO: BAR
          - FOO: PIYO
    runs-on: ubuntu-latest
    steps:
      # Expanding object at 'env:' section
      - run: echo "$FOO"
        env: ${{ matrix.env_object }}
      # String value cannot be expanded as object
      - run: echo "$FOO"
        env: ${{ matrix.env_string }}

Output:

test.yaml:19:14: type of expression at "env" must be object but found type string [expression]
   |
19 |         env: ${{ matrix.env_string }}
   |              ^~~

Playground

In above example, environment variables mapping is expanded at env: section. actionlint checks type of the expanded value.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      # Access to undefined context
      - run: echo '${{ unknown_context }}'
      # Access to undefined property of context
      - run: echo '${{ github.events }}'
      # Calling undefined function (start's'With is correct)
      - run: echo "${{ startWith('hello, world', 'lo,') }}"
      # Wrong number of arguments
      - run: echo "${{ startsWith('hello, world') }}"
      # Wrong type of parameter
      - run: echo "${{ startsWith('hello, world', github.event) }}"
      # Function overloads can be handled properly. contains() has string version and array version
      - run: echo "${{ contains('hello, world', 'lo,') }}"
      - run: echo "${{ contains(github.event.labels.*.name, 'enhancement') }}"
      # format() has special check for formating string
      - run: echo "${{ format('{0}{1}', 1, 2, 3) }}"

Output:

test.yaml:7:24: undefined variable "unknown_context". available variables are "env", "github", "job", "matrix", "needs", "runner", "secrets", "steps", "strategy" [expression]
  |
7 |       - run: echo '${{ unknown_context }}'
  |                        ^~~~~~~~~~~~~~~
test.yaml:9:24: property "events" is not defined in object type {workspace: string; env: string; event_name: string; event_path: string; ...} [expression]
  |
9 |       - run: echo '${{ github.events }}'
  |                        ^~~~~~~~~~~~~
test.yaml:11:24: undefined function "startWith". available functions are "always", "cancelled", "contains", "endswith", "failure", "format", "fromjson", "hashfiles", "join", "startswith", "success", "tojson" [expression]
   |
11 |       - run: echo "${{ startWith('hello, world', 'lo,') }}"
   |                        ^~~~~~~~~~~~~~~~~
test.yaml:13:24: number of arguments is wrong. function "startsWith(string, string) -> bool" takes 2 parameters but 1 arguments are given [expression]
   |
13 |       - run: echo "${{ startsWith('hello, world') }}"
   |                        ^~~~~~~~~~~~~~~~~~
test.yaml:15:51: 2nd argument of function call is not assignable. "object" cannot be assigned to "string". called function type is "startsWith(string, string) -> bool" [expression]
   |
15 |       - run: echo "${{ startsWith('hello, world', github.event) }}"
   |                                                   ^~~~~~~~~~~~~
test.yaml:20:24: format string "{0}{1}" does not contain placeholder {2}. remove argument which is unused in the format string [expression]
   |
20 |       - run: echo "${{ format('{0}{1}', 1, 2, 3) }}"
   |                        ^~~~~~~~~~~~~~~~

Playground

Contexts and built-in functions are strongly typed. Typos in property access of contexts and function names can be checked. And invalid function calls like wrong number of arguments or type mismatch at parameter also can be checked thanks to type checker.

The semantics checker can properly handle that

• some functions are overloaded (e.g. contains(str, substr) and contains(array, item))
• some parameters are optional (e.g. join(strings, sep) and join(strings))
• some parameters are repeatable (e.g. hashFiles(file1, file2, ...))

In addition, format() function has special check for placeholders in the first parameter which represents formatting string.

Note that context names and function names are case insensitive. For example, toJSON and toJson are the same function.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    outputs:
      # Step outputs can be used in job outputs since this section is evaluated after all steps were run
      foo: '${{ steps.get_value.outputs.name }}'
    steps:
      # Access to undefined step outputs
      - run: echo '${{ steps.get_value.outputs.name }}'
      # Outputs are set here
      - run: echo '::set-output name=foo::value'
        id: get_value
      # OK
      - run: echo '${{ steps.get_value.outputs.name }}'
      # OK
      - run: echo '${{ steps.get_value.conclusion }}'
  other:
    runs-on: ubuntu-latest
    steps:
      # Access to undefined step outputs. Step objects are job-local
      - run: echo '${{ steps.get_value.outputs.name }}'

Output:

test.yaml:10:24: property "get_value" is not defined in object type {} [expression]
   |
10 |       - run: echo '${{ steps.get_value.outputs.name }}'
   |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.yaml:22:24: property "get_value" is not defined in object type {} [expression]
   |
22 |       - run: echo '${{ steps.get_value.outputs.name }}'
   |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Playground

Outputs of step can be accessed via steps.<step_id> objects. The steps context is dynamic:

• Accessing to the outputs before running the step are null
• Outputs of steps only in the job can be accessed. It cannot access to steps across jobs

It is actually common mistake to access to the wrong step outputs since people often forget fixing placeholders on copying&pasting steps.

actionlint can catch the invalid accesses to step outputs and reports them as errors.

Example input:

on: push
jobs:
  test:
    strategy:
      matrix:
        os: [ubuntu-latest, windows-latest]
        node: [14, 15]
        package:
          - name: 'foo'
            optional: true
          - name: 'bar'
            optional: false
        include:
          - node: 15
            npm: 7.5.4
    runs-on: ${{ matrix.os }}
    steps:
      # Access to undefined matrix value
      - run: echo '${{ matrix.platform }}'
      # Matrix value is strongly typed. Below line causes an error since matrix.package is {name: string, optional: bool}
      - run: echo '${{ matrix.package.dev }}'
      # OK
      - run: |
          echo 'os: ${{ matrix.os }}'
          echo 'node version: ${{ matrix.node }}'
          echo 'package: ${{ matrix.package.name }} (optional=${{ matrix.package.optional }})'
      # Additional matrix values in 'include:' are supported
      - run: echo 'npm version is specified'
        if: ${{ contains(matrix.npm, '7.5') }}
  test2:
    runs-on: ubuntu-latest
    steps:
      # Matrix values in other job is not accessible
      - run: echo '${{ matrix.os }}'

Output:

test.yaml:19:24: property "platform" is not defined in object type {os: string; node: number; package: {name: string; optional: bool}; npm: string} [expression]
   |
19 |       - run: echo '${{ matrix.platform }}'
   |                        ^~~~~~~~~~~~~~~
test.yaml:21:24: property "dev" is not defined in object type {name: string; optional: bool} [expression]
   |
21 |       - run: echo '${{ matrix.package.dev }}'
   |                        ^~~~~~~~~~~~~~~~~~
test.yaml:34:24: property "os" is not defined in object type {} [expression]
   |
34 |       - run: echo '${{ matrix.os }}'
   |                        ^~~~~~~~~

Playground

Types of matrix context is contextually checked by the semantics checker. Type of matrix values in matrix: section is deduced from element values of its array. When the matrix value is an array of objects, objects' properties are checked strictly like package.name in above example.

When type of the array elements is not persistent, type of the matrix value falls back to any.

strategy:
  matrix:
    foo:
      - 'string value'
      - 42
      - {aaa: true, bbb: null}
    bar:
      - [42]
      - [true]
      - [{aaa: true, bbb: null}]
      - []
steps:
  # matrix.foo is any type value
  - run: echo ${{ matrix.foo }}
  # matrix.bar is array<any> type value
  - run: echo ${{ matrix.bar[0] }}

Example input:

on: push
jobs:
  install:
    outputs:
      installed: '...'
    runs-on: ubuntu-latest
    steps:
      - run: echo 'install something'
  prepare:
    outputs:
      prepared: '...'
    runs-on: ubuntu-latest
    steps:
      - run: echo 'parepare something'
      # ERROR: Outputs in other job is not accessble
      - run: echo '${{ needs.prepare.outputs.prepared }}'
  build:
    needs: [install, prepare]
    outputs:
      built: '...'
    runs-on: ubuntu-latest
    steps:
      # OK: Accessing to job results
      - run: echo 'build something with ${{ needs.install.outputs.installed }} and ${{ needs.prepare.outputs.prepared }}'
      # ERROR: Accessing to undefined output cases an error
      - run: echo '${{ needs.install.outputs.foo }}'
      # ERROR: Accessing to undefined job ID
      - run: echo '${{ needs.some_job }}'
  other:
    runs-on: ubuntu-latest
    steps:
      # ERROR: Cannot access to outptus across jobs
      - run: echo '${{ needs.build.outputs.built }}'

Output:

test.yaml:16:24: property "prepare" is not defined in object type {} [expression]
   |
16 |       - run: echo '${{ needs.prepare.outputs.prepared }}'
   |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.yaml:26:24: property "foo" is not defined in object type {installed: string} [expression]
   |
26 |       - run: echo '${{ needs.install.outputs.foo }}'
   |                        ^~~~~~~~~~~~~~~~~~~~~~~~~
test.yaml:28:24: property "some_job" is not defined in object type {install: {outputs: {installed: string}; result: string}; prepare: {outputs: {prepared: string}; result: string}} [expression]
   |
28 |       - run: echo '${{ needs.some_job }}'
   |                        ^~~~~~~~~~~~~~
test.yaml:33:24: property "build" is not defined in object type {} [expression]
   |
33 |       - run: echo '${{ needs.build.outputs.built }}'
   |                        ^~~~~~~~~~~~~~~~~~~~~~~~~

Playground

Job dependencies can be defined at needs:. A job runs after all jobs defined in needs: are done. Outputs from the jobs can be accessed only from jobs following them via needs context.

actionlint defines type of needs variable contextually looking at each job's outputs: section and needs: section.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: echo $FOO
  test-win:
    runs-on: windows-latest
    steps:
      # Shell on Windows is PowerShell by default.
      # shellcheck is not run in this case.
      - run: echo $FOO
      # This script is run with bash due to 'shell:' configuration
      - run: echo $FOO
        shell: bash

Output:

test.yaml:6:9: shellcheck reported issue in this script: SC2086:info:1:6: Double quote to prevent globbing and word splitting [shellcheck]
  |
6 |       - run: echo $FOO
  |         ^~~~
test.yaml:14:9: shellcheck reported issue in this script: SC2086:info:1:6: Double quote to prevent globbing and word splitting [shellcheck]
   |
14 |       - run: echo $FOO
   |         ^~~~

shellcheck is a famous linter for ShellScript. actionlint runs shellcheck for scripts at run: step in workflow. For installing shellcheck, see the official installation document.

actionlint detects which shell is used to run the scripts following the documentation. On Linux or macOS, the default shell is bash and on Windows it is pwsh. Shell can be configured by shell: configuration at workflow level or job level. Each step can configure shell to run scripts by shell:.

actionlint remembers the default shell and checks what OS the job runs on. Only when the shell is bash or sh, actionlint applies shellcheck to scripts.

By default, actionlint checks if shellcheck command exists in your system and uses it when it is found. The -shellcheck option on running actionlint command specifies the executable path of shellcheck. Setting empty string by shellcheck= disables shellcheck integration explicitly.

Since both ${{ }} expression syntax and ShellScript's variable access $FOO use $, remaining ${{ }} confuses shellcheck. To avoid it, actionlint replaces ${{ }} with underscores. For example echo '${{ matrix.os }}' is replaced with echo '________________'.

Example input:

on: push
jobs:
  linux:
    runs-on: ubuntu-latest
    steps:
      # Yay! No error
      - run: print('${{ runner.os }}')
        shell: python
      # ERROR: Undefined variable
      - run: print(hello)
        shell: python
  linux2:
    runs-on: ubuntu-latest
    defaults:
      run:
        # Run script with Python by default
        shell: python
    steps:
      - run: |
          import sys
          for sys in ['system1', 'system2']:
            print(sys)
      - run: |
          from time import sleep
          print(100)

Output:

test.yaml:10:9: pyflakes reported issue in this script: 1:7 undefined name 'hello' [pyflakes]
   |
10 |       - run: print(hello)
   |         ^~~~
test.yaml:19:9: pyflakes reported issue in this script: 2:5 import 'sys' from line 1 shadowed by loop variable [pyflakes]
   |
19 |       - run: |
   |         ^~~~
test.yaml:23:9: pyflakes reported issue in this script: 1:1 'time.sleep' imported but unused [pyflakes]
   |
23 |       - run: |
   |         ^~~~

Python script can be written in run: when shell: python is configured.

pyflakes is a famous linter for Python. It is suitable for linting small code like scripts at run: since it focuses on finding mistakes (not a code style issue) and tries to make false positives as minimal as possible. Install pyflakes by pip install pyflakes.

actionlint runs pyflakes for scripts at run: steps in workflow and reports errors found by pyflakes. actionlint detects Python scripts in workflow by checking shell: python at steps and defaults: configurations at workflows and jobs.

By default, actionlint checks if pyflakes command exists in your system and uses it when found. The -pyflakes option of actionlint command allows to specify the executable path of pyflakes. Setting empty string by pyflakes= disables pyflakes integration explicitly.

Since both ${{ }} expression syntax is invalid as Python, remaining ${{ }} might confuse pyflakes. To avoid it, actionlint replaces ${{ }} with underscores. For example print('${{ matrix.os }}') is replaced with print('________________').

Example input:

on: push
jobs:
  prepare:
    needs: [build]
    runs-on: ubuntu-latest
    steps:
      - run: echo 'prepare'
  install:
    needs: [prepare]
    runs-on: ubuntu-latest
    steps:
      - run: echo 'install'
  build:
    needs: [install]
    runs-on: ubuntu-latest
    steps:
      - run: echo 'build'

Output:

test.yaml:8:3: cyclic dependencies in "needs" configurations of jobs are detected. detected cycle is "install" -> "prepare", "prepare" -> "build", "build" -> "install" [job-needs]
  |
8 |   install:
  |   ^~~~~~~~

Playground

Job dependencies can be defined at needs:. If cyclic dependencies exist, jobs never start to run. actionlint detects cyclic dependencies in needs: sections of jobs and reports it as error.

actionlint also detects undefined jobs and duplicate jobs in needs: section.

Example input:

on: push
jobs:
  foo:
    needs: [bar, BAR]
    runs-on: ubuntu-latest
    steps:
      - run: echo 'hi'
  bar:
    needs: [unknown]
    runs-on: ubuntu-latest
    steps:
      - run: echo 'hi'

Output:

test.yaml:4:18: job ID "BAR" duplicates in "needs" section. note that job ID is case insensitive [job-needs]
  |
4 |     needs: [bar, BAR]
  |                  ^~~~
test.yaml:8:3: job "bar" needs job "unknown" which does not exist in this workflow [job-needs]
  |
8 |   bar:
  |   ^~~~

Playground

Example input:

on: push
jobs:
  test:
    strategy:
      matrix:
        node: [10, 12, 14, 14]
        os: [ubuntu-latest, macos-latest]
        exclude:
          - node: 13
            os: ubuntu-latest
          - node: 10
            platform: ubuntu-latest
    runs-on: ${{ matrix.os }}
    steps:
      - run: echo ...

Output:

test.yaml:6:28: duplicate value "14" is found in matrix "node". the same value is at line:6,col:24 [matrix]
  |
6 |         node: [10, 12, 14, 14]
  |                            ^~~
test.yaml:9:19: value "13" in "exclude" does not exist in matrix "node" combinations. possible values are "10", "12", "14", "14" [matrix]
  |
9 |           - node: 13
  |                   ^~
test.yaml:12:13: "platform" in "exclude" section does not exist in matrix. available matrix configurations are "node", "os" [matrix]
   |
12 |             platform: ubuntu-latest
   |             ^~~~~~~~~

Playground

matrix: defines combinations of multiple values. Nested include: and exclude: can add/remove specific combination of matrix values. actionlint checks

• values in exclude: appear in matrix: or include:
• duplicate in variations of matrix values

Example input:

on:
  push:
    # Unexpected filter. 'branches' is correct
    branch: foo
  issues:
    # Unexpected type. 'opened' is correct
    types: created
  pullreq:

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: echo ...

Output:

test.yaml:4:5: unexpected key "branch" for "push" section. expected one of "types", "branches", "branches-ignore", "tags", "tags-ignore", ... [syntax-check]
  |
4 |     branch: foo
  |     ^~~~~~~
test.yaml:7:12: invalid activity type "created" for "issues" Webhook event. available types are "opened", "edited", "deleted", "transferred", ... [events]
  |
7 |     types: created
  |            ^~~~~~~
test.yaml:8:3: unknown Webhook event "pullreq". see https://docs.github.com/en/actions/reference/events-that-trigger-workflows#webhook-events for list of all Webhook event names [events]
  |
8 |   pullreq:
  |   ^~~~~~~~

Playground

At on:, Webhook events can be specified to trigger the workflow. Webhook event documentation defines which Webhook events are available and what types can be specified at types: for each event.

actionlint validates the Webhook configurations:

• unknown Webhook event name
• unknown type for Webhook event
• invalid filter names

Example input:

on:
  push:
    branches:
      # ^ is not available for branch name. This kind of mistake is usually caused by misunderstanding
      # that regular expression is available here
      - '^foo-'
    tags:
      # Invalid syntax. + cannot follow special character *
      - 'v*+'
      # Invalid character range 9-1
      - 'v[9-1]'

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: echo ...

Output:

test.yaml:6:10: character '^' is invalid for branch and tag names. ref name cannot contain spaces, ~, ^, :, [, ?, *. see `man git-check-ref-format` for more details. note that regular expression is unavailable. note: filter pattern syntax is explained at https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#filter-pattern-cheat-sheet [glob]
  |
6 |       - '^foo-'
  |          ^~~~~~
test.yaml:9:12: invalid glob pattern. unexpected character '+' while checking special character + (one or more). the preceding character must not be special character. note: filter pattern syntax is explained at https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#filter-pattern-cheat-sheet [glob]
  |
9 |       - 'v*+'
  |            ^~
test.yaml:11:14: invalid glob pattern. unexpected character '1' while checking character range in []. start of range '9' (57) is larger than end of range '1' (49). note: filter pattern syntax is explained at https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#filter-pattern-cheat-sheet [glob]
   |
11 |       - 'v[9-1]'
   |              ^~~

Playground

For filtering branches, tags and paths in Webhook events, glob syntax is available. actionlint validates glob patterns branches:, branches-ignore:, tags:, tags-ignore:, paths:, paths-ignore: in a workflow. It checks:

• syntax errors like missing closing brackets for character range [..]
• invalid usage like ? following *, invalid character range [9-1], ...
• invalid character usage for Git ref names (branch name, tag name)
  • ref name cannot start/end with /
  • ref name cannot contain [, :, \, ...

Most common mistake I have ever seen here is misunderstanding that regular expression is available for filtering. This rule can catch the mistake so that users can notice their mistakes.

Example input:

on:
  schedule:
    # Cron syntax is not correct
    - cron: '0 */3 * *'
    # Interval of scheduled job is too small (job runs too frequently)
    - cron: '* */3 * * *'

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: echo ...

Output:

test.yaml:4:13: invalid CRON format "0 */3 * *" in schedule event: Expected exactly 5 fields, found 4: 0 */3 * * [events]
  |
4 |     - cron: '0 */3 * *'
  |             ^~
test.yaml:6:13: scheduled job runs too frequently. it runs once per 60 seconds [events]
  |
6 |     - cron: '* */3 * * *'
  |             ^~

Playground

To trigger a workflow in specific interval, scheduled event can be defined in POSIX CRON syntax.

actionlint checks the CRON syntax and frequency of running the job. When a job is run more frequently than once per 1 minute, actionlint reports it as error.

Example input:

on: push
jobs:
  test:
    strategy:
      matrix:
        runner:
          # OK
          - macos-latest
          # ERROR: Unknown runner
          - linux-latest
          # OK: Preset labels for self-hosted runner
          - [self-hosted, linux, x64]
          # OK: Single preset label for self-hosted runner
          - arm64
          # ERROR: Unknown label "gpu". Custom label must be defined in actionlint.yaml config file
          - gpu
    runs-on: ${{ matrix.runner }}
    steps:
      - run: echo ...

  test2:
    # ERROR: Too old macOS worker
    runs-on: macos-10.13
    steps:
      - run: echo ...

Output:

test.yaml:10:13: label "linux-latest" is unknown. available labels are "windows-latest", "windows-2019", "windows-2016", "ubuntu-latest", ... [runner-label]
   |
10 |           - linux-latest
   |             ^~~~~~~~~~~~
test.yaml:16:13: label "gpu" is unknown. available labels are "windows-latest", "windows-2019", "windows-2016", "ubuntu-latest", ... [runner-label]
   |
16 |           - gpu
   |             ^~~
test.yaml:23:14: label "macos-10.13" is unknown. available labels are "windows-latest", "windows-2019", "windows-2016", "ubuntu-latest", ... [runner-label]
   |
23 |     runs-on: macos-10.13
   |              ^~~~~~~~~~~

Playground

GitHub Actions provides two kinds of job runners, GitHub-hosted runner and self-hosted runner. Each runner has one or more labels. GitHub Actions runtime finds a proper runner based on label(s) specified at runs-on: to run the job. So specifying proper labels at runs-on: is important.

actionlint checks proper label is used at runs-on: configuration. Even if an expression is used in the section like runs-on: ${{ matrix.foo }}, actionlint parses the expression and resolves the possible values, then validates the values.

When you define some custom labels for your self-hosted runner, actionlint does not know the labels. Please set the label names in actionlint.yaml configuration file to let actionlint know them.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      # ERROR: ref is missing
      - uses: actions/checkout
      # ERROR: owner name is missing
      - uses: checkout@v2
      # ERROR: tag is empty
      - uses: 'docker://image:'
      # ERROR: local action does not exist
      - uses: ./github/actions/my-action

Output:

test.yaml:7:15: specifying action "actions/checkout" in invalid format because ref is missng. available formats are "{owner}/{repo}@{ref}" or "{owner}/{repo}/{path}@{ref}" [action]
  |
7 |       - uses: actions/checkout
  |               ^~~~~~~~~~~~~~~~
test.yaml:9:15: specifying action "checkout@v2" in invalid format because owner is missing. available formats are "{owner}/{repo}@{ref}" or "{owner}/{repo}/{path}@{ref}" [action]
  |
9 |       - uses: checkout@v2
  |               ^~~~~~~~~~~
test.yaml:11:15: tag of Docker action should not be empty: "docker://image" [action]
   |
11 |       - uses: 'docker://image:'
   |               ^~~~~~~~~~~~~~~~~
test.yaml:13:15: Neither action.yaml nor action.yml is found in directory "github/actions/my-action" [action]
   |
13 |       - uses: ./github/actions/my-action
   |               ^~~~~~~~~~~~~~~~~~~~~~~~~~

Playground

Action needs to be specified in a format defined in the document. There are 3 types of actions:

• action hosted on GitHub: owner/repo/path@ref
• local action: ./path/to/my-action
• Docker action: docker://image:tag

actionlint checks values at uses: sections follow one of these formats.

My action definition at .github/actions/my-action/action.yaml:

name: 'My action'
author: 'rhysd <https://rhysd.github.io>'
description: 'my action'

inputs:
  name:
    description: your name
    default: anonymous
  message:
    description: message to this action
    required: true
  addition:
    description: additional information
    required: false

runs:
  using: 'node14'
  main: 'index.js'

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      # missing required input "message"
      - uses: ./.github/actions/my-action
      # unexpected input "additions"
      - uses: ./.github/actions/my-action
        with:
          name: rhysd
          message: hello
          additions: foo, bar

Output:

test.yaml:7:15: missing input "message" which is required by action "My action" defined at "./.github/actions/my-action" [action]
  |
7 |       - uses: ./.github/actions/my-action
  |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~
test.yaml:13:11: input "additions" is not defined in action "./.github/actions/my-action" defined at "My action". available inputs are "addition", "message", "name" [action]
   |
13 |           additions: foo, bar
   |           ^~~~~~~~~~

When a local action is run in uses: of step:, actionlint reads action.yaml file in the local action directory and validates inputs at with: in the workflow are correct. Missing required inputs and unexpected inputs can be detected.

Example input:

on: push
jobs:
  linux:
    runs-on: ubuntu-latest
    steps:
      - run: echo 'hello'
        # ERROR: Unavailable shell
        shell: dash
      - run: echo 'hello'
        # ERROR: 'powershell' is only available on Windows
        shell: powershell
      - run: echo 'hello'
        # OK: 'powershell' is only available on Windows
        shell: powershell
  mac:
    runs-on: macos-latest
    defaults:
      run:
        # ERROR: default config is also checked. fish is not supported
        shell: fish
    steps:
      - run: echo 'hello'
        # OK: Custom shell
        shell: 'perl {0}'
  windows:
    runs-on: windows-latest
    steps:
      - run: echo 'hello'
        # ERROR: 'sh' is only available on Windows
        shell: sh

Output:

test.yaml:8:16: shell name "dash" is invalid. available names are "bash", "pwsh", "python", "sh" [shell-name]
  |
8 |         shell: dash
  |                ^~~~
test.yaml:11:16: shell name "powershell" is invalid on macOS or Linux. available names are "bash", "pwsh", "python", "sh" [shell-name]
   |
11 |         shell: powershell
   |                ^~~~~~~~~~
test.yaml:14:16: shell name "powershell" is invalid on macOS or Linux. available names are "bash", "pwsh", "python", "sh" [shell-name]
   |
14 |         shell: powershell
   |                ^~~~~~~~~~
test.yaml:20:16: shell name "fish" is invalid. available names are "bash", "pwsh", "python", "sh" [shell-name]
   |
20 |         shell: fish
   |                ^~~~
test.yaml:30:16: shell name "sh" is invalid on Windows. available names are "bash", "pwsh", "python", "cmd", "powershell" [shell-name]
   |
30 |         shell: sh
   |                ^~

Playground

Available shells for runners are defined in the documentation. actionlint checks shell names at shell: configuration are properly using the available shells.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: echo 'hello'
        id: step_id
      - run: echo 'bye'
        # ERROR: Duplicate of step ID
        id: STEP_ID
  # ERROR: Duplicate of job ID
  TEST:
    runs-on: ubuntu-latest
    steps:
      - run: echo 'hello'
        # OK. Step ID uniqueness is job-local
        id: step_id

Output:

test.yaml:10:13: step ID "STEP_ID" duplicates. previously defined at line:7,col:13. step ID must be unique within a job. note that step ID is case insensitive [step-id]
   |
10 |         id: STEP_ID
   |             ^~~~~~~
test.yaml:12:3: key "test" is duplicate in "jobs" section. previously defined at line:3,col:3. note that key names are case insensitive [syntax-check]
   |
12 |   TEST:
   |   ^~~~~

Playground

Job IDs and step IDs in each job must be unique. IDs are compared in case insensitive. actionlint checks all job IDs and step IDs and reports errors when some IDs duplicate.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    container:
      image: 'example.com/owner/image'
      credentials:
        username: user
        # ERROR: Hardcoded password
        password: pass
    services:
      redis:
        image: redis
        credentials:
          username: user
          # ERROR: Hardcoded password
          password: pass
    steps:
      - run: echo 'hello'

Output:

test.yaml:10:19: "password" section in "container" section should be specified via secrets. do not put password value directly [credentials]
   |
10 |         password: pass
   |                   ^~~~
test.yaml:17:21: "password" section in "redis" service should be specified via secrets. do not put password value directly [credentials]
   |
17 |           password: pass
   |                     ^~~~

Playground

Credentials for container can be put in container: configuration. Password should be put in secrets and the value should be expanded with ${{ }} syntax at password:. actionlint checks hardcoded credentials and reports them as error.

Example input:

on: push
jobs:
  test:
    runs-on: ubuntu-latest
    env:
      FOO=BAR: foo
      FOO BAR: foo
    steps:
      - run: echo 'hello'

Output:

test.yaml:6:7: environment variable name "foo=bar" is invalid. '&', '=' and spaces should not be contained [env-var]
  |
6 |       FOO=BAR: foo
  |       ^~~~~~~~
test.yaml:7:7: environment variable name "foo bar" is invalid. '&', '=' and spaces should not be contained [env-var]
  |
7 |       FOO BAR: foo
  |       ^~~

Playground

= must not be included in environment variable names. And & and spaces should not be included in them. In almost all cases they are mistakes and they may cause some issues on using them in shell since they have special meaning in shell syntax.

actionlint checks environment variable names are correct in env: configuration.

Configuration file actionlint.yaml or actionlint.yml can be put in .github directory.

You don't need to write first configuration file by your hand. actionlint command can generate a default configuration.

actionlint -init-config
vim .github/actionlint.yaml

Since the author tries to keep configuration file as minimal as possible, currently only one item can be configured.

self-hosted-runner:
  # Labels of self-hosted runner in array of string
  labels:
    - linux.2xlarge
    - windows-latest-xl
    - linux-multi-gpu

• self-hosted-runner: Configuration for your self-hosted runner environment
  • labels: Label names added to your self-hosted runners as list of string

Note that configuration file is optional. The author tries to keep configuration file as minimal as possible not to bother users to configure behavior of actionlint. Running actionlint without configuration file would work fine in most cases.

actionlint can be used from Go programs. See the documentation to know the list of all APIs. It contains workflow file parser built on top of go-yaml/yaml, expression ${{ }} lexer/parser/checker, etc. Followings are unexhaustive list of interesting APIs.

• Command struct represents entire actionlint command. Command.Main takes command line arguments and runs command until the end and returns exit status.
• Linter manages linter lifecycle and applies checks to given files. If you want to run actionlint checks in your program, please use this struct.
• Project and Projects detect a project (Git repository) in a given directory path and find configuration in it.
• Config represents structure of actionlint.yaml config file. It can be decoded by go-yaml/yaml library.
• Workflow, Job, Step, ... are nodes of workflow syntax tree. Workflow is a root node.
• Parse() parses given contents into a workflow syntax tree. It tries to find syntax errors as much as possible and returns found errors as slice.
• Pass is a visitor to traverse a workflow syntax tree. Multiple passes can be applied at single pass using Visitor.
• Rule is an interface for rule checkers and RuneBase is a base struct to implement a rule checker.
  • RuleExpression is a rule checker to check expression syntax in ${{ }}.
  • RuleShellcheck is a rule checker to apply shellcheck command to run: sections and collect errors from it.
  • RuleJobNeeds is a rule checker to check dependencies in needs: section. It can detect cyclic dependencies.
  • ...
• ExprLexer lexes expression syntax in ${{ }} and returns slice of Token.
• ExprParser parses given slice of Token and returns syntax tree for expression in ${{ }}. ExprNode is an interface for nodes in the expression syntax tree.
• ExprType is an interface of types in expression syntax ${{ }}. ObjectType, ArrayType, StringType, NumberType, ... are structs to represent actual types of expression.
• ExprSemanticsChecker checks semantics of expression syntax ${{ }}. It traverses given expression syntax tree and deduces its type, checking types and resolving variables (contexts).
• ValidateRefGlob() and ValidatePathGlob() validate glob filter pattern and returns all errors found by the validator.

Note that the version of this repository is for command line tool actionlint. So it does not represent version of the library, meant that patch version bump may introduce some breaking changes.

• All examples in 'Checks' section are tested in example_test.go
• I cloned GitHub top 1000 repositories and extracted 1400+ workflow files. And I tried actionlint with the collected workflow files. All bugs found while the trial were fixed and I confirmed no more false positives.

When you 're seeing some bugs or false positives, it is helpful to file a new issue with a minimal example of input. Giving me some feedbacks like feature requests or idea of additional checks is also welcome.

• Repository: https://github.com/rhysd/actionlint
• Playground: https://rhysd.github.io/actionlint/
• GitHub Actions official documentations
  • Workflow syntax: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions
  • Expression syntax: https://docs.github.com/en/actions/reference/context-and-expression-syntax-for-github-actions
  • Built-in functions: https://docs.github.com/en/actions/reference/context-and-expression-syntax-for-github-actions#functions
  • Webhook events: https://docs.github.com/en/actions/reference/events-that-trigger-workflows#webhook-events
  • Self-hosted runner: https://docs.github.com/en/actions/hosting-your-own-runners/about-self-hosted-runners
• CRON syntax: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/crontab.html#tag_20_25_07
• shellcheck: https://github.com/koalaman/shellcheck
• pyflakes: https://github.com/PyCQA/pyflakes
• Japanese blog post for this project: https://rhysd.hatenablog.com/entry/2021/07/11/214313

actionlint is distributed under the MIT license.