YAML Validator
Validate YAML with exact line and column errors, plus the warnings a pass/fail check hides.
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How to Validate YAML
Paste a manifest, pipeline, or configuration file. The validator reports the first syntax error with its line and column, then - for a document that parses - the root type, the number of documents if the file contains several separated by ---, and any parser warnings. Every check runs locally, so credentials sitting in an environment block never leave the tab.
Why Duplicate Keys Matter
A YAML file with the same key twice in one mapping is legal enough to parse: the later value overwrites the earlier one without complaint. In a CI pipeline that means the environment variable, image tag, or replica count you carefully set at the top of the file can be silently discarded by a copy-pasted block further down. This validator surfaces those as warnings, which a plain "valid YAML" badge never does.
| Input | Output | Note |
|---|---|---|
| \tkey: value | Error: tabs not allowed | Use spaces |
| a: 1\na: 2 | Warning: duplicate key | a becomes 2 |
| key: [1, 2 | Error: unexpected end | Unclosed flow sequence |
| on: push | Valid; on parses as a string in YAML 1.2 | YAML 1.1 read it as true |
Frequently Asked Questions
Which YAML version is validated?
YAML 1.2, the version used by Kubernetes, Docker Compose, GitHub Actions, GitLab CI, and Ansible. Errors are reported with the line and column where the parser stopped.
What does the warning section show?
Problems that parse successfully but are almost always bugs - most importantly duplicate mapping keys, where the last value silently wins and quietly overrides the configuration you thought you set. Deprecated tag syntax and unresolvable tags are also reported there.
Why is my indentation an error?
YAML forbids tabs for indentation; only spaces are allowed. A tab that looks correct in your editor is a hard parse error. Inconsistent indentation within one block is the other frequent cause - every key in a mapping must start at the same column.
Does valid YAML mean my Kubernetes manifest is correct?
No. Valid YAML means the file parses into a document. Whether that document has the fields Kubernetes, Compose, or Actions requires is schema validation against the specific tool, which this validator does not attempt and does not claim.
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