YAML Validator

Check whether YAML is well-formed and pinpoint syntax errors.

ToolsSoup's YAML Validator is a free online tool that instantly checks whether your YAML is well-formed and, when it is not, points you to the line of the first syntax error with a clear explanation. Everything runs in your browser — no uploads, no sign-up, and your data never leaves your device.

What is a YAML validator?

A YAML validator parses your document and checks that it follows YAML's syntax rules: consistent indentation with spaces (never tabs), a colon after every mapping key, properly closed quotes and flow collections, and correctly nested mappings and sequences. If the YAML is valid you get a confirmation with a quick summary of the top-level structure; if not, the validator reports the line of the first problem so you can fix it fast.

How to validate YAML online

Validating YAML with ToolsSoup takes just a few seconds:

  1. Paste or type your YAML into the input box.
  2. Click Validate to check it against YAML's syntax rules.
  3. Read the result: a green confirmation, or a red message with the line of the first error.

Common YAML mistakes

Most invalid YAML comes down to a handful of recurring issues. Knowing them makes errors quick to fix:

  1. Using tabs for indentation — YAML only accepts spaces.
  2. Inconsistent indentation between sibling keys or list items.
  3. A missing colon after a mapping key, or no space after the colon.
  4. Unclosed quotes or unbalanced flow collections like [a, b or {x: 1.

Why use this YAML validator?

  • 100% free with no ads, sign-up, or usage limits.
  • Runs entirely in your browser — your data is never uploaded to a server.
  • Pinpoints the line of the first syntax error.
  • Confirms valid YAML and summarizes the top-level structure.
  • Great for Docker Compose, Kubernetes, GitHub Actions, and Ansible files.

Frequently asked questions

Is this YAML validator free?

Yes. Every tool on ToolsSoup is completely free to use, with no account, sign-up, or hidden limits.

Is my YAML data safe?

Absolutely. All validation happens locally in your browser using JavaScript, so your YAML is never sent to or stored on any server.

Why does it say my YAML is invalid?

The most common causes are tabs used for indentation, inconsistent indentation, a missing colon after a key, or an unclosed quote or flow collection. The line in the error points you to the first issue.

Does it validate against a schema?

No. This tool checks that your YAML is well-formed — syntactically correct. It does not validate against a JSON Schema or any specific structure, which is a separate step.

Why can't I use tabs to indent YAML?

The YAML specification forbids tab characters for indentation to avoid ambiguity, since tab width varies between editors. Always indent with spaces — two spaces per level is the common convention.