yamllint-ts

A TypeScript implementation of yamllint, the YAML linter.

Installation

npm install yamllint-ts

Usage

# Lint a file
yamllint-ts myfile.yaml

# Lint with a config file
yamllint-ts -c .yamllint.yaml myfile.yaml

# Lint with inline config
yamllint-ts -d '{extends: relaxed, rules: {line-length: {max: 120}}}' myfile.yaml

Configuration

yamllint-ts uses the same configuration format as Python yamllint. See the yamllint documentation for details.

Compatibility with Python yamllint

yamllint-ts aims for full feature parity with Python yamllint. All linting rules are implemented and produce identical results for valid YAML files.

Parser Differences

yamllint-ts uses the yaml package for YAML parsing, while Python yamllint uses PyYAML. These parsers have different error reporting behavior for malformed YAML:

| Aspect | Python yamllint (PyYAML) | yamllint-ts (eemeli/yaml) | |--------|--------------------------|---------------------------| | Error messages | PyYAML-style messages (e.g., "could not find expected ':'") | yaml-style messages (e.g., "Implicit keys need to be on a single line") | | Error positions | May differ by 1-2 lines | May differ by 1-2 lines | | Error detection | Detects some errors earlier/later in parsing | Detects some errors earlier/later in parsing |

Example

For this YAML with no_space_after:value on line 3 (missing space after colon):

---
good: value
no_space_after:value
extra_spaces:   value

• Python yamllint: 4:1 error syntax error: could not find expected ':'
• yamllint-ts: 3:1 error syntax error: Implicit keys need to be on a single line

Both correctly identify the file as invalid, but with different error messages and line numbers.

Impact

• For valid YAML: 100% parity - all rules produce identical results
• For malformed YAML: Syntax errors are detected but may have different messages/positions
• Comparison testing: 144/160 tests match (90%), with all differences being syntax error reporting

Why Not Use PyYAML?

Porting PyYAML's scanner (~2000 lines of Python) to TypeScript would be a significant undertaking. The current approach provides full linting functionality while leveraging a well-maintained, modern YAML parser. The trade-off of slightly different syntax error messages for invalid YAML was deemed acceptable.

Rules

All yamllint rules are supported:

• anchors
• braces
• brackets
• colons
• commas
• comments
• comments-indentation
• document-end
• document-start
• empty-lines
• empty-values
• float-values
• hyphens
• indentation
• key-duplicates
• key-ordering
• line-length
• new-line-at-end-of-file
• new-lines
• octal-values
• quoted-strings
• trailing-spaces
• truthy

License

GPL-3.0 (same as Python yamllint)

Attribution

This project is a TypeScript port of yamllint by Adrien Vergé, licensed under GPL-3.0. The original Python implementation provided the design, rules, and test cases that this port is based on.