What this YAML validator checks
- Syntax — indentation, unclosed quotes and brackets, invalid block scalars.
- Duplicate keys — a classic source of silent bugs in Kubernetes and docker-compose files.
- Tabs — YAML forbids tab indentation; the error points to the exact line.
- Multi-document files — each
---section is parsed and listed with itskindand name.
YAML to JSON and back
The right panel shows your YAML converted to JSON (an array if the file has several documents). Switch the output to YAML (normalized) to get a cleanly re-indented version with comments and anchors resolved. To go the other way, paste JSON and click JSON → YAML.
Gotchas worth knowing
| You write | YAML reads it as |
|---|---|
version: 1.10 | the number 1.1 — quote versions: "1.10" |
port: 08080 | a number; leading zeros are lost — quote it |
key: yes | in YAML 1.2 the string "yes", in YAML 1.1 tools (some older parsers) the boolean true |
time: 12:30 | a string in YAML 1.2, but sexagesimal 750 in YAML 1.1 parsers |
Frequently asked questions
Does this validate Kubernetes manifests?
It validates YAML syntax for any file, including multi-document Kubernetes manifests separated by ---. For each document it also shows the detected apiVersion, kind and metadata.name so you can quickly confirm what the file contains. It does not check fields against the Kubernetes API schema.
Why does my YAML fail with “duplicated mapping key”?
The same key appears twice in one mapping, e.g. two “env:” blocks in one container. Many tools silently keep the last value, which hides bugs, so this validator reports it as an error.
Can I use tabs for indentation in YAML?
No. The YAML specification forbids tab characters for indentation. Use spaces (2 is the most common convention).
Which YAML version is supported?
YAML 1.2 via the js-yaml library, the same parser used by many Node.js tools.
Is my YAML uploaded anywhere?
No. Validation and conversion run entirely in your browser, so it is safe to paste configs that contain internal hostnames or secrets.