GitHub Actions Expression Evaluator

GitHub Actions expressions (${{ }}) control conditional steps, set outputs, and format strings in your workflows. But testing them requires pushing code and waiting for a workflow run. This tool lets you evaluate expressions locally with custom context values — so you can verify your if: conditions, string functions, and status checks before committing.

What You Can Evaluate

The evaluator supports the full GitHub Actions expression syntax:

• Literals — true, false, null, numbers, strings
• Operators — ==, !=, &&, ||, !, <, >, <=, >=
• Functions — contains(), startsWith(), endsWith(), format(), join(), toJSON(), fromJSON(), hashFiles() (simulated)
• Status functions — success(), failure(), cancelled(), always()
• Context access — github.event_name, env.MY_VAR, steps.build.outputs.result, matrix.os

Setting Up Contexts

Define custom context values in JSON format to simulate different scenarios:

{
  "github": {
    "event_name": "pull_request",
    "ref": "refs/heads/feature/login",
    "actor": "octocat"
  },
  "env": {
    "NODE_ENV": "production",
    "DEPLOY_TARGET": "staging"
  },
  "steps": {
    "build": {
      "outputs": { "result": "success" },
      "outcome": "success"
    }
  }
}

Then test expressions like:

• github.event_name == 'push' → false
• contains(github.ref, 'feature/') → true
• steps.build.outputs.result == 'success' && env.NODE_ENV == 'production' → true

How to Use

1. Enter your expression in the expression input (without the ${{ }} wrapper)
2. Define context values as JSON in the context panel
3. See the evaluated result instantly
4. Adjust contexts to test different scenarios

Frequently Asked Questions

Does it support the hashFiles() function? hashFiles() is simulated — it returns a deterministic hash based on the input string. In real GitHub Actions, it hashes actual file contents from the repository.

Can I test matrix expressions? Yes. Define a matrix object in your context JSON (e.g., {"matrix": {"os": "ubuntu-latest", "node": 18}}) and reference it as matrix.os or matrix.node.

How do status functions work here? You can set step outcomes in the context (steps.stepId.outcome) and the status functions will evaluate based on those values. always() always returns true.

Is my expression sent to a server? No. All evaluation runs in your browser using a JavaScript expression parser. No data leaves your device.

What’s the difference between this and the GitHub Actions Validator? The validator checks your entire workflow YAML for structural correctness. This tool focuses on evaluating individual expressions against custom context data.