YAML 1.2 core · every document

Free online YAML validator and formatter

Paste YAML to check syntax, duplicate keys and every document, then format valid input. Parsing stays in your browser.

Open YAMLCheck

No upload · no execution · no JSON conversion

Three checks

Paste, inspect, format

01

Parse YAML 1.2 core

All documents use one named schema.

02

Read line and column

Up to 100 issues stay visible.

03

Format only valid input

Parsed comments remain in YAML output.

Configuration review

Useful before a parser or deployment sees the file

  • Find an accidental duplicate key.
  • Count documents in a stream.
  • Inspect anchor and alias use.
  • Normalize layout without losing comments.

Reproducible YAML

Try a config and an alias fixture

Find duplicate keys and positioned syntax errors, inspect documents and format valid YAML without uploading it.
View examples

YAML 1.2 · browser only

Validate the whole YAML stream

Find duplicate keys and positioned syntax errors, inspect documents and format valid YAML without uploading it.

Open YAMLCheck