What does the validator actually check?

It runs your input through a full YAML 1.2 parser and reports whether parsing succeeds. It's a syntax check, not a schema check: it confirms the document is structurally valid YAML, not that it matches a particular application's expected shape (a Kubernetes manifest, a GitHub Actions workflow, and so on).

Why does my YAML fail here but work in my editor's YAML plugin?

Editor plugins vary widely in strictness, and some silently tolerate things the spec doesn't allow, like tabs used for indentation or duplicate keys in a mapping. This validator uses a spec-compliant parser, so it will catch issues a more lenient tool might not flag.

What's the most common YAML mistake this catches?

Indentation errors, by a wide margin: a key indented one space more or less than its siblings, or tabs mixed with spaces. YAML uses indentation to express structure the way braces do in JSON, so a single misaligned line can make an entire block parse incorrectly or fail outright.

Does the validator send my document anywhere?

No. Parsing happens entirely in your browser, so nothing about the document, including whether it's valid, is sent to a server.

YAML Validator - Check YAML Syntax Online

Overview

Introduction

YAML's indentation-based syntax is easy to get subtly wrong: one misaligned space can turn a mapping into something else entirely, often without an obviously broken-looking result. This validator answers one question directly, does this text parse as valid YAML, and points at exactly where it doesn't.

It's most useful the moment something downstream, a CI pipeline, a Helm release, an app's config loader, rejects a file with a vague error. Running the same document through a dedicated validator usually surfaces the real problem faster than the tool that failed to load it.

What Is YAML Validator?

A YAML validator parses input with a real, spec-compliant YAML 1.2 parser and reports success or the precise location of the first syntax error, rather than guessing or partially rendering broken input.

For valid input it also reports a few structural facts: whether the document's root is a mapping, sequence, or scalar, how deeply it's nested, and its size in bytes.

How YAML Validator Works

The tool attempts a full parse of your input. On success, it walks the resulting value to compute depth and, for mappings and sequences, a key or item count. On failure, it reports the parser's own error location.

Because validation runs client-side, there's no request size limit imposed by a server, only your browser's available memory.

When To Use YAML Validator

Use it whenever a YAML-consuming tool fails with a confusing error and you want to isolate whether the file itself is malformed before looking anywhere else.

It's also useful as a quick sanity check before committing a hand-edited config file, or after generating YAML programmatically.

Often used alongside YAML Formatter & Prettifier and YAML Minifier.

Features

Advantages

Runs entirely client-side, so sensitive config never leaves your browser.
Points to the exact line and column of the first syntax error.
Reports basic structural stats for valid documents at no extra step.
Uses a spec-compliant parser, so it catches issues looser tools might miss.

Limitations

This checks syntax only, not whether the document matches a particular schema or application's expected fields.
Only the first document in a multi-document (`---`-separated) stream is validated.
Duplicate keys are permitted rather than flagged, matching this parser's default, lenient behavior.

Examples

Valid document

Input

id: 1
name: Ada Lovelace
roles:
  - admin
  - editor

Output

Valid YAML. Type: object, Depth: 2, Keys: 3

The document parses successfully as a mapping with three top-level keys.

Indentation error

Invalid input

a: b
  c: d

Parser error

Nested mappings are not allowed in compact mappings at line 1, column 4:

A key indented under a plain scalar value is not valid YAML structure, and the parser reports exactly where it gave up.

Corrected version

a: b
c: d

Best Practices & Notes

Best Practices

Validate a document immediately after hand-editing it, before committing or deploying.
Run generated YAML through the validator once after changing the code that produces it, not just the templates.
If a downstream tool's error message is unhelpful, validate the raw file here first to rule out a syntax problem.

Developer Notes

This wraps the `yaml` package's `parse()` in a try/catch and reports either the parsed value's shape or the thrown `YAMLParseError`'s `linePos` and `pos` fields, translated into the same line/column/position error shape every tool on this site uses. No schema validation library is involved, this is a pure syntax check.

YAML Validator Use Cases

Diagnosing a CI pipeline that rejects a YAML config with an unclear error
Sanity-checking a hand-edited Kubernetes manifest before applying it
Confirming programmatically generated YAML is well-formed
Checking a YAML snippet pasted from documentation or a chat message before reusing it

Common Mistakes

Mixing tabs and spaces for indentation, which is invalid in YAML's block structure.
Assuming a file that loads in one tool is valid everywhere, when different parsers vary in strictness.
Treating a validator pass as proof the data matches the shape your application expects, when it only confirms the syntax parses.

Tips

Use the reported line and column to jump straight to the offending line in your editor.
If validation passes but your application still rejects the file, the issue is almost certainly a schema mismatch, not syntax.
Pair this with the YAML Formatter once your document is valid, to make its structure easier to review.

YAML Validator