YAML Tools
YAML Validator
Check whether a YAML document can be parsed as configuration data. Find indentation mistakes, duplicate keys, and unsupported values with a location you can jump to in the editor.
✓ Every tool runs in your browser. We do not upload your input or output.
Keyboard shortcuts
Ctrl/⌘ + Enter: process
Ctrl/⌘ + Shift + F: full screen
Esc: exit full screen
Ctrl/⌘ + F in editor: search
How to use
- Paste a YAML document, upload a file, or load the sample configuration.
- Wait for validation, or press Process when the file is larger than 1 MB.
- If an error appears, select it to move the editor cursor to the reported line and column.
- Correct the document and run validation again before copying the result.
Examples
Check a normal configuration
A mapping with nested number and boolean values parses successfully.
service: port: 8080 enabled: true
Valid YAML
Find a repeated key
The second key is reported because its value would otherwise be ambiguous.
port: 8080 port: 9090
duplicated mapping key (line 2, column 1)
Catch YAML mistakes before using a file
A configuration can appear readable while still failing to parse. A missing closing bracket, a sequence item aligned at the wrong level, or a duplicate key may prevent a build or change which value wins. The validator checks one YAML document and gives a clear result. When the parser can locate a problem, the error includes a line and column. Select the error to jump to that position in the input editor.
The reported position is a starting point for investigation. A missing colon on one line can make the next line look wrong, and an unclosed flow list may only be detected at the end of the document. Check the lines immediately before the marker as well. After editing, press Process or use Ctrl/Command + Enter to run the check again.
Scope of validation
This tool validates YAML syntax and values that the site’s converters can represent consistently. It accepts mappings, sequences, ordinary scalar values, and non-circular aliases. It rejects duplicate mapping keys, unsupported custom tags, circular aliases, and non-finite numbers. It does not know whether a particular port, image, or timeout field is correct for your application. For that, use the application’s schema or configuration test after this syntax check.
Large documents are parsed in a Web Worker so the page stays responsive. The workspace keeps its height when errors or output change, and the input panel scrolls independently. The tool processes your pasted text or uploaded file locally; no processing backend receives its contents.
Frequently asked questions
Does valid YAML mean my application will accept it?
No. This checks YAML syntax and the supported data types, not the field names or schema required by an application.
Does it accept multiple documents in one stream?
No. Validate each document separately when a file uses document separators.
Are anchors allowed?
Ordinary anchors and aliases are accepted, but a circular alias cannot be converted to the site's data model.
Are custom tags or special numeric values allowed?
Custom tags and non-finite numbers are rejected so this validator agrees with the YAML converters.
Where is validation performed?
It runs in your browser. The document is not sent to a server for processing.