YAML Formatter & Validator
Format YAML with comments and anchors retained. Validate and download multi-document files.
This tool runs entirely in your browser. Your data is never uploaded, never stored, and never leaves your device.
Format and validate supported YAML while retaining comments, anchors and multi-document boundaries, with local copy and download.
How to use it
- 1Paste YAML or open a .yaml or .yml file.
- 2Choose indentation, then validate or format the document.
- 3Review the output and copy or download the YAML file.
What happens to your data
YAML stays on your device. No public sharing URL is created and no application configuration is applied.
Last updated October 2026
Format YAML while retaining the comments, anchors and separate documents that explain how a configuration works. Paste YAML or open a local .yaml or .yml file, choose two or four spaces, and inspect the formatted result before copying or downloading it. Validation reports syntax problems without applying the configuration anywhere.
A YAML formatter should not silently throw away a deployment note. Converting YAML into an ordinary object and dumping it back often loses comments and rewrites scalar values. This formatter works with the document syntax instead. It preserves comments, anchors, aliases and exact number spellings while making supported layout consistent. It can handle several documents separated by --- in one input.
Formatting, syntax validation and application validation solve different problems. Valid YAML can still be an invalid Kubernetes manifest, GitHub Actions workflow or Docker Compose configuration. This page does not know the fields, versions or permissions expected by those applications. Run their own validator before deployment; formatting alone does not show that a configuration is safe or correct.
How it works
The input is checked within a bounded YAML 1.2 core subset and formatted using the browser version of Prettier. The formatter is loaded only when needed. Custom tags and complex mapping keys are unsupported here. Aliases are retained rather than expanded into a much larger document. Choose Format for readable layout or Validate when you want a syntax check without generating a different file.
Comments, multi-document boundaries and scalar meaning are the priorities, not byte-for-byte identity. Quotes, line wrapping, whitespace and final newline style can change; downloads use UTF-8 and LF line endings. Changing the source or formatting settings clears the old result so Copy and Download cannot quietly export earlier content.
Bounds are 500,000 pasted characters, a 500,000-byte file, 100 documents, 60 nesting levels and 50 aliases per document. These limits help keep browser processing responsive. A valid document in another YAML dialect or using a custom tag may still be rejected. No remote schema, include or application endpoint is fetched, and the contents are not placed in a shareable URL.
Worked example: format a two-document configuration
- Input
- # deployment service: {replicas: 2, port: 8080} --- # job job: {enabled: true}
- Result
- Two YAML documents remain, with both comments, replicas 2, port 8080 and enabled true preserved.
Formatting can change presentation. Validation of these keys for a real application remains that application's responsibility.
Common use cases
- Making a commented deployment configuration easier to review
- Checking syntax across a multi-document YAML file
- Retaining anchors and explanatory notes during formatting
- Downloading a consistently indented local copy without publishing the configuration
Frequently asked questions
Does this YAML formatter keep comments?＋
Yes. Formatting uses the document syntax instead of a YAML-to-object-to-YAML conversion. Header notes, inline comments and comments between documents are retained, although surrounding layout can change.
Can I format multiple YAML documents together?＋
Yes. Documents separated by --- are processed together, up to 100 documents. Their order and boundaries remain. The validator checks each supported document rather than silently ignoring everything after the first.
Does valid YAML mean my Kubernetes or Compose file will work?＋
No. YAML syntax is only the file format. The target application's schema, version and runtime rules require its own validator. This tool neither deploys nor verifies those application rules.
Does this expand anchors and aliases?＋
No. Formatting retains anchors and aliases. It bounds the number of aliases instead of expanding them into repeated data. Custom tags and complex keys are not supported by this page's validation subset.
Why did the output change quotes or line endings?＋
A formatter normalises presentation. Supported scalar meanings and comments are preserved, but quote choice, wrapping, indentation and newline style can change. Downloaded files use UTF-8 and LF line endings.
Is my YAML uploaded or saved at a public link?＋
No. The selected file or pasted text is processed in your browser, and this tool does not create a public sharing URL. Keep your original file and review the output before using it.
Standards and limitations
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