YAML Preflight

Free

Free browser-based YAML checker that catches GitHub Actions permission mistakes

Unlimited Free Tier

Free plan checked against YAML Preflight's pricing page on 8 September 2026. Re-checked monthly.

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About YAML Preflight

YAML Preflight is a small validation tool that catches YAML which parses fine locally but breaks GitHub Actions. It checks strict YAML syntax, duplicate same-level keys, YAML 1.2 boolean quirks, and a documented subset of invalid GitHub Actions permission values, up to 100 KB per document. Everything runs client side in the browser, so pasted YAML is never uploaded, and there is no signup, checkout, or payment. The page also shows a $9 per month repository monitor as a stated proposal that is not built yet, used only to gauge interest, so it has no bearing on the free checker itself.

Key Features

Runs entirely in the browser, YAML never leaves the client

Built-in example checks for common failure patterns

Scoped findings tied to GitHub Actions permissions reference

Pros & Cons

Genuinely free, no signup or payment anywhere in the flow

Local-only processing, good for sensitive workflow files

Local checker source is MIT-licensed on GitHub

Manual, one document at a time, no automation

Narrow scope focused on GitHub Actions permission mistakes

The proposed repository monitor is not built yet

The free plan in practice

What you can actually do on YAML Preflight's free plan (Unlimited manual checks, up to 100 KB per document), where it stops, and when it's worth paying.

What you can do free

Unlimited manual YAML checks up to 100 KB
Strict YAML syntax validation
Duplicate same-level key detection
YAML 1.2 boolean behavior checks
Selected GitHub Actions permission mistake detection

Where it stops

Manual paste only, no repository or CI integration
100 KB document size limit
Does not claim full GitHub Actions workflow-schema validation

When to upgrade to a paid plan

Stay on the free plan while you're comfortably under the free plan's limit (Unlimited manual checks, up to 100 KB per document). It's worth moving to a paid plan once you consistently bump into that ceiling, need to remove branding, or want features the free tier holds back.