YAML Validator
This YAML validator checks YAML strictly against YAML 1.2: syntax errors and duplicate keys with their line number, plus a note when anchors, merge keys, custom tags or comments are present.
What you get
- Validate YAML online against YAML 1.2, with the line of every error: a YAML lint that also finds duplicate keys.
- Points out anchors, custom tags, non-string keys and several documents that other tools may read differently.
- Valid YAML is shown formatted, with comments, anchors and tags kept.
- A YAML syntax checker for any file, and a Kubernetes YAML validator for syntax: multiple documents separated by --- are checked one by one.
- Private and free: everything runs in your browser, nothing is uploaded, and there is no sign-up.
How each result is checked
- Parsed strictly as YAML 1.2 (core schema): duplicate keys and syntax errors are reported with the line.
- Valid YAML is shown formatted, with comments, anchors and tags kept, and that output is checked to hold the same documents, values, types, tags and comments.
What can't convert exactly
- YAML 1.1 tools (some older libraries) read words like yes, no, on and off as booleans; YAML 1.2 reads them as strings.
Questions
Does it validate Kubernetes or docker-compose files?
It checks the YAML itself. For the structure of a specific file type, generate or use a JSON Schema and the JSON Schema converters.
Is my data uploaded?
No. Everything runs in your browser, in a background worker. Nothing is sent to a server.
Can it validate Kubernetes YAML, docker-compose files and GitHub Actions workflows?
It checks their YAML syntax: indentation, duplicate keys, unclosed quotes and lists, and several documents separated by ---. Whether the keys are the right ones for Kubernetes or GitHub Actions is a separate check against that tool’s JSON Schema.
Why did a duplicate key pass in another tool?
Many YAML readers keep the last value and say nothing. The YAML 1.2 spec says keys must be unique, so this validator reports duplicates with their line.
How do I use the YAML Validator online?
Paste your input or open a file on the left. The result appears on the right as you type, already checked; copy or download it. Nothing is uploaded: the YAML Validator runs in your browser.