yaml-lint

YAML structural validator with friendly error messages. Catches the mistakes people actually make: tabs in indentation, missing space after colons, unbalanced quotes/brackets, duplicate keys, trailing whitespace. Zero dependencies.

Unlike yamllint (Python), this works wherever Node.js does. Unlike full YAML parsers, this is fast and needs no install.

Install

npm install -g yaml-lint

Or without installing:

npx yaml-lint

Usage

yaml-lint                          # Lint all .yaml/.yml in current dir
yaml-lint config.yaml              # Lint a single file
yaml-lint .github/workflows/       # Lint a directory
yaml-lint --format github          # GitHub Actions annotations
yaml-lint --strict                 # Exit 1 on warnings too

Example Output

yaml-lint  3 file(s) scanned

  ✗ config/app.yaml
      4:5    error    Tab character in indentation (use spaces)  (indentation)
      8:12   error    Missing space after ':' in mapping  (colon-space)
      15:1   error    Duplicate key 'name' at this indentation  (duplicate-key)
      22:1   warning  Trailing whitespace  (trailing-whitespace)

  ! .github/workflows/ci.yml
      3:1    warning  Missing '---' at start of document  (document-start)

  1 clean · 3 errors · 2 warnings

Rules

| Rule | Severity | Description | |---|---|---| | indentation | error | Tab character in indentation | | colon-space | error | Missing space after : in mapping | | duplicate-key | error | Same key appears twice at the same level | | flow-brackets | error | Unbalanced [] or {} | | unbalanced-quotes | error | Unbalanced quote characters | | line-length | warning | Line exceeds 120 chars | | trailing-whitespace | warning | Trailing spaces/tabs | | final-newline | warning | Missing newline at end of file | | document-start | warning | Missing --- (only with --doc-start) |

CI Integration

GitHub Actions:

- name: Lint YAML
  run: npx yaml-lint --format github --strict

Exit code is 1 if any errors are found (or warnings, with --strict).

Options

| Flag | Default | Description | |---|---|---| | --max-line-length <N> | 120 | Warn for lines longer than N | | --doc-start | off | Require --- at start | | --allow-tabs | off | Allow tab characters | | --no-final-newline | off | Don't require trailing newline | | --format <fmt> | human | human, json, github | | --strict | off | Exit 1 on warnings too | | --quiet | off | Only show files with issues |

License

MIT

Keywords

yaml linter · yaml validator · yamllint alternative · validate yaml · lint yaml · yaml ci · github actions yaml · check yaml · zero dependencies · cli

Built to solve, shared to help — Rushabh Shah 🛠️✨

One of 40+ zero-dependency developer CLI tools — no node_modules, ever.