YAML Tools

YAML Validator

Full YAML 1.2 validation with the exact line and column of every error — catch the indent bug before your pipeline does.

In short

A YAML validator parses a document with a full YAML 1.2 parser — anchors resolved, scalars typed — and reports the exact line and column of the first error. That matters more in YAML than in JSON because indentation is the syntax: a mis-indented key does not error, it silently attaches to the wrong parent, and a tab breaks the parse entirely.

By NaveenKumar T · Updated 18 Sep 2026

Learn: YAML Multi-line Strings: | vs > vs Quoted (Indentation Rules)

Exact error line & column
Full YAML 1.2 parsing
Anchors & aliases resolved

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Example

YAML Validator: input and output

A GitHub Actions-style CI pipeline — the kind of file where a single misplaced space silently breaks a job trigger.

Input · yaml

name: build-and-test
on: [push, pull_request]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: npm ci
      - run: npm test
env:
  NODE_ENV: test

Output · yaml

name: build-and-test
on:
  - push
  - pull_request
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - run: npm ci
      - run: npm test
env:
  NODE_ENV: test

Validation re-serializes in canonical block style — the flow-style on: [push, pull_request] list comes back as two dashed lines — proof the document parsed cleanly.

Learn more

Why YAML validation matters more than most

YAML powers the configs that break deployments: Kubernetes manifests, GitHub Actions, docker-compose, Ansible. Unlike JSON, where errors are loud, YAML often fails SILENTLY — a mis-indented key doesn't error, it just attaches to the wrong parent and your option is quietly ignored. Validating before committing catches both loud and silent failures.

This validator runs a complete YAML 1.2 parse — the same operation your tooling performs — with anchors resolved and scalars typed, so a green badge here means the document will load everywhere.

The errors that bite in practice

Tabs in indentation (invisible and illegal), a colon inside an unquoted value (image: nginx:latest needs no quote, but title: Deploy: prod does), unquoted values that change type (country code NO becoming boolean false in YAML 1.1 tooling), and block scalars (| and >) indented one space off. Each produces a precise position here instead of a cryptic CI failure.

Help

Frequently asked questions

Everything you need to know about the YAML Validator.

01How do I use the YAML Validator?

Paste your YAML — a Kubernetes manifest, CI pipeline, docker-compose file — and click Validate. Valid documents get a green badge and normalized output; broken ones report the precise position of the first problem.

02My YAML looks fine but the validator rejects it — why?

Ninety percent of the time: a tab character used for indentation (YAML forbids tabs — they look identical to spaces), inconsistent indent depth within one block, or a missing space after a colon (key:value instead of key: value). The reported column points at the exact offending character.

03Why is the error position so important in YAML validation specifically?

Because whitespace IS the syntax, so a validator that only says 'invalid' leaves you re-reading the whole file. A single space too many silently reassigns which mapping a key belongs to; a tab breaks the parse entirely. This validator reports the exact line and column of the first problem and underlines it in the editor, so a 400-line manifest with one bad indent is a one-glance fix instead of a search.

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