Side Quest: Using gh aw compile to Catch Errors Early

Optional: take this detour if you want a deeper walkthrough of gh aw compile, then return to Step 7 or Step 9.

:dart: What You'll Do

You'll use gh aw compile as a fast feedback loop while you edit workflow files. By the end, you'll know when to use --no-emit for dry-run checks, when to use --validate for targeted troubleshooting, when to keep --watch running, and how to fix the most common compile errors.

What gh aw compile does

gh aw compile checks your workflow source file, validates the frontmatter and Markdown body structure, and generates the compiled lock file GitHub Actions runs. It catches formatting and schema mistakes before you commit or trigger a workflow.

Run it any time you edit a workflow file:

gh aw compile

If it succeeds, you should see a green success message and an updated .lock.yml file beside your source file.

Use --no-emit for quick structure checks

When you only want a yes/no answer without generating a lock file, use --no-emit:

gh aw compile --no-emit

This is useful after each small edit because it confirms the file structure without writing or overwriting the generated lock file every time.

Troubleshoot with --validate

Use plain gh aw compile for normal workflow edits. If you need targeted troubleshooting or an explicit schema/deprecation audit, add --validate:

gh aw compile --validate

This enables GitHub Actions workflow schema validation, container image validation, and action SHA validation. It is more thorough than a plain compile but also slower, so reserve it for those focused checks instead of routine compile loops.

Use --watch while you iterate

If you're still editing by hand, keep the compiler running:

gh aw compile --watch

Each save triggers another compile, so you get immediate feedback instead of discovering YAML mistakes later.

How to read a compile error

When gh aw compile fails, start with the first line number it reports. YAML errors are often caused by the line above or below the reported line, especially when indentation is off.

The examples below show gh-aw source files before compilation, so values like schedule: daily and schedule: daily on weekdays are valid shorthand here. The error is the indentation, not the schedule value itself.

---
# ❌ Broken — "workflow_dispatch" is not nested under "on:"
on:
  schedule: daily
workflow_dispatch: {}
---

---
# ✅ Fixed
on:
  schedule: daily
  workflow_dispatch: {}
---

---
# ❌ Broken — "schedule" is not indented under "on:"
on:
schedule: daily on weekdays
  workflow_dispatch: {}
---

---
# ✅ Fixed
on:
  schedule: daily on weekdays
  workflow_dispatch: {}
---

Quick fixes for common compile errors

If you see this kind of error	Usually means	Check this first
YAML parse error or did not find expected key	A key is indented at the wrong level	Make sure nested keys under on:, permissions:, tools:, or safe-outputs: are indented two more spaces than their parent
found character that cannot start any token	You pasted a tab character or stray YAML punctuation	Replace tabs with spaces and check for accidental special characters in unquoted values
unexpected end of stream or frontmatter/document errors	The frontmatter fences are incomplete	Confirm the file has both the opening --- and the closing --- for the frontmatter
A section that worked before suddenly fails after one edit	The newest edit changed nearby YAML structure	Re-check the last block you touched before reading the rest of the file

✅ Checkpoint

• I know what gh aw compile checks before a workflow runs
• I can use --no-emit for quick structure checks without generating a lock file
• I can use --watch for live feedback while I edit
• I can spot indentation mistakes in a compile error example
• I know the first places to check when compilation fails

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Return to: Step 7 — Your First Workflow | Step 9 — Agentic Editing