GitHub Actions trigger explainer

Know which GitHub Actions workflows will fire — and exactly why the others won't — before you push.

Name: actwhy
Author: actwhy

Paste your GitHub Actions YAML, simulate a push or pull request, and get an instant, honest verdict for every workflow — down to the exact filter or if: condition that stops it. Runs entirely in your browser.

npx actwhy

Star on GitHub

FIRES SKIPPED UNKNOWN Three verdicts, one lit lamp — never a guess.

# workflows

Load an example

Workflow YAML

Simulated event

Branch

Changed files

One path per line. Leave blank = files unknown → actwhy returns UNKNOWN for any paths filter instead of guessing.

Advanced — commit message

Commit message

Used by conditions like contains(github.event.head_commit.message, '[skip ci]').

# verdict re-evaluated live

Why didn't my GitHub Actions workflow run?

The loop

Kill the push-debug-push loop

Stop committing “fix trigger 🙏”, pushing, waiting for the runner, and finding nothing ran. Whether it's a paths filter that isn't matching, a branches pattern, or an if: condition — actwhy answers before you push, in milliseconds, offline.

The rule

Three-valued honesty

When it can't know — the changed files aren't specified, a matrix is dynamic — it says UNKNOWN, not maybe. actwhy never guesses.

The engine

GitHub's own parser

Built on @actions/workflow-parser and @actions/expressions — the same MIT-licensed libraries GitHub uses to read your YAML and evaluate ${{ }}.

How it compares to act and actionlint

act

Runs your workflows locally in Docker to actually execute the jobs.

executes

actwhy

Explains the trigger decision instantly — which workflows fire, and the exact reason the rest don't.

explains

actionlint

Lints workflow syntax and catches static mistakes in your YAML.

lints

Complementary tools — actwhy answers the one question the others don't: will it even trigger?

Install the CLI