Does this validator upload my Maestro flow?

No. The validator runs entirely in your browser using js-yaml. No network requests are made with your flow content. You can verify this by opening DevTools → Network tab while validating.

What does the Maestro YAML validator check?

YAML syntax errors with line and column numbers, missing or empty appId, unknown commands (typos like tapON instead of tapOn), unrecognized selector keys, unknown config keys, hardcoded secrets in env, AI commands that incur cost or non-determinism, and flow length warnings.

Is this the same parser Maestro uses?

Yes. The validator uses js-yaml — the same YAML parser Maestro itself uses — so syntax errors caught here will match what Maestro reports at runtime.

DeviceLab · Free Tools

Maestro .yaml Validator

Name: Maestro YAML Validator
Author: DeviceLab

Catch broken flows before they hit a device. Paste a flow, drop a file, or load one — get syntax errors, unknown commands, and missing config flagged instantly.

Runs 100% in your browser — nothing uploaded

flow.yaml

Results

⌘

Validate a flow to see results here.
Everything stays on this page.

What this tool checks

YAML syntax errors (with line + column)
Missing or empty appId
Unknown commands (typos like tapON instead of tapOn)
Unrecognized selector keys inside tapOn, assertVisible, etc.
Unknown keys in the config document
Hardcoded secrets in env (passwords, tokens, API keys)
AI commands that incur cost or non-determinism in CI
Flow length warnings (recommends splitting at 60+ steps)

Why we built this

Most Maestro flow errors get caught only when a CI run fails. Validating locally in the browser turns a 5-minute CI round-trip into a 50-millisecond check. The validator uses the same YAML parser Maestro itself uses (js-yaml), and the command list is kept in sync with the open-source Maestro spec.

About DeviceLab

We build the open-source maestro-runner — a faster, JVM-free Maestro CLI — and a managed device cloud that runs your Maestro and Appium tests on real devices you own. See what DeviceLab does →