YAML Validator

YAML is a human-friendly data format used for configuration files, CI pipelines, Kubernetes manifests, and Docker Compose setups. Its biggest strength is also its biggest trap: whitespace and indentation carry meaning, so a single misplaced space or a stray tab can break a whole file. A YAML validator catches those mistakes before they reach your build.

ToolHub YAML Validator parses your input as you type. If it is valid, you get a clear success status and a normalized, re-formatted version with consistent indentation. If it is invalid, you get the exact parser error, including the line and column when available. Everything happens in your browser.

1. 1

   Paste your YAML

   Drop your YAML into the input panel. The validator runs automatically on every keystroke, so there is no button to press.
2. 2

   Read the status

   A green Valid YAML badge means the document parses cleanly. A red Invalid YAML badge means the parser hit a problem.
3. 3

   Copy the cleaned output

   When the input is valid, the output panel shows a normalized version with 2-space indentation. Click Copy to grab it.

The tool loads your text with a full YAML parser. Parsing succeeds only when the document follows the YAML spec: correct indentation, balanced quotes and brackets, valid anchors, and no duplicate keys in a mapping. When parsing succeeds, the parsed value is dumped back to YAML, which is why the output is re-formatted and consistent.

Why indentation matters so much

YAML uses indentation to express structure, the way Python uses it for blocks. Mixing tabs and spaces, or indenting a list item by the wrong amount, changes what the document means or makes it invalid. The validator surfaces these issues with a line and column reference so you can jump straight to the problem.

Normalized output

The cleaned output uses uniform 2-space indentation and a canonical layout. This is handy when you have inherited a messy file with inconsistent spacing or inline collections like [png, jpg, webp] that you want expanded into a tidy, predictable shape.

• Use spaces, never tabs. Most YAML parsers reject tab indentation outright.
• Keep indentation consistent. Two spaces per level is the common convention.
• Quote strings that contain colons, hashes, or that look like numbers or booleans you want kept as text.
• Watch for duplicate keys in a mapping. Strict parsers treat them as an error.
• When in doubt, validate early and often rather than waiting for a failed deploy.

Why does my file fail with a tab error?

YAML does not allow tabs for indentation. Replace every leading tab with spaces. Many editors can show whitespace characters or convert tabs to spaces automatically.

What do the numbers in the error mean?

The parser reports the line and column where it gave up, usually shown as (line:column). That points you at the spot to inspect, though the real cause is sometimes a line or two above it.

Is the output the same as my input?

It is the same data, but re-formatted. Comments are dropped and formatting is normalized because the tool re-dumps the parsed value. The structure and values are preserved.

Can it validate multiple documents in one file?

This tool validates a single YAML document. For multi-document files separated by ---, validate each document on its own.