YAML Validator

Validate YAML syntax and quickly catch indentation or syntax errors.

A lightweight first check for YAML

YAML looks simple, yet one stray tab or a missing space after a colon can stop a Docker Compose file or CI pipeline from loading. This validator scans your text for the two most common beginner mistakes and points to the exact line, so you can fix them before running the real tool.

Validating your YAML

Paste your document into the Input Data box. Sample loads a Docker Compose snippet with a web and db service.
Click Process / Generate.
The badge above the result turns to Valid or Invalid. When problems exist, a red list shows one entry per issue and the summary counts the errors detected.
If everything passes, the text is shown again with keys and list items lightly coloured. Use Copy or Download to save it as result.txt.

The two checks it makes

Tab characters: YAML forbids tabs for indentation, so any line containing a tab is reported.
Space after colon: on each line, it looks at the first colon and reports the line if the next character is not a space, for example key:value.

Blank lines and comment lines are skipped.

Typical uses

Debugging a docker-compose.yml that refuses to start after an editor inserted tabs.
Checking a GitHub Actions or GitLab CI file pasted from a chat message.
Screening application config before committing to a repository.
Learning why YAML rejects a value that looked fine to the eye.

How far to trust a green result

This is a heuristic scanner, not a full parser, and the interface calls a passing result structurally valid, not fully valid. It does not check that indentation is consistent, that keys are unique, that quotes and brackets are balanced, or that anchors resolve. It can also raise false alarms: a list item such as a bare URL, or a line like a time value written 12:30, has a colon followed by a non-space and will be flagged even though it is legitimate. Only the first colon on each line is examined. When the tool says Valid, still run the file through your real toolchain, for example docker compose config or a language YAML library, for a definitive answer. The scan runs in JavaScript in the browser page.

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Frequently Asked Questions

What errors does the YAML Validator detect?

It reports lines containing tab characters and lines where the first colon is not followed by a space. Each message includes the line number. It does not test indentation consistency, duplicate keys or unbalanced quotes.

Why was a valid URL line flagged as an error?

The checker looks at the first colon on each line. A bare list item like a URL starting with https: has a slash after the colon, not a space, so it is reported. If your value is quoted or follows a key with a space, it passes.

Does Valid mean my YAML will load without problems?

Not necessarily. The tool only confirms that its two heuristic checks passed. Inconsistent indentation, repeated keys or an unclosed quote can still break loading. Confirm with your real parser, such as docker compose config or your language's YAML library.

Can it point me to the exact position of a mistake?

It gives the line number for each issue but not a column. Open the line in your editor and look for a tab or a colon directly followed by text. Enable visible whitespace in your editor to make tabs easier to spot.

Can I keep the highlighted result?

Yes. When the input passes, use Copy to take the text or Download to save it as result.txt. When errors are found, the same buttons save the error list rather than a corrected document.