yamllint

1.38.0 · active · verified Sun Mar 29

yamllint is a linter for YAML files written in Python, version 1.38.0. It checks not only for syntax validity but also for common weirdnesses like key repetition and cosmetic issues such as line length, trailing spaces, and indentation. The project is actively maintained with regular releases.

Warnings

breaking yamllint has progressively dropped support for older Python versions. As of 1.38.0, Python 3.9 is no longer supported, and Python 3.8 was dropped in 1.36.0. Users on older Python environments will need to upgrade their Python version or use an older yamllint version.
Fix: Upgrade Python to 3.10+ or pin `yamllint` to an older compatible version.
gotcha By default, the `yamllint` CLI exits with code 1 only if errors are found, not warnings. This can lead to CI/CD pipelines passing silently even with warnings. To make warnings also cause a non-zero exit code, use the strict mode.
Fix: Run `yamllint` with the `--strict` (or `-s`) option in CI/CD environments: `yamllint --strict .`
gotcha yamllint automatically discovers and loads configuration files named `.yamllint`, `.yamllint.yaml`, or `.yamllint.yml` in the current working directory or any parent directory. This implicit loading can lead to unexpected linting rules being applied if a configuration file exists upstream that you are unaware of or did not intend to use.
Fix: Explicitly specify a configuration file using the `-c` option (`yamllint -c /path/to/myconfig.yaml file.yaml`) or disable automatic config search for specific use cases. Be aware of your project's directory structure for `.yamllint` files.
breaking The API for `linter.run` experienced a change in version 1.35.0 regarding how file ignoration was handled, which was then reverted in 1.35.1. If you programmatically interact with `linter.run` and rely on specific file path handling or ignoration behavior, this version range could introduce unexpected results.
Fix: Avoid `yamllint` version 1.35.0 if programmatic file ignoration is critical; upgrade to 1.35.1 or newer, or downgrade to 1.34.x or older.

Install

pip install yamllint Install with pip

Imports

YamlLintConfig

from yamllint.config import YamlLintConfig

linter
```
from yamllint import linter
```
LintProblem
```
from yamllint.linter import LintProblem
```
Represents a detected linting issue; returned by `linter.run`.

Quickstart

This quickstart demonstrates how to programmatically lint a YAML string using `yamllint`. It creates a `YamlLintConfig` and then uses `linter.run` with an `io.StringIO` object to process the YAML content, iterating over any `LintProblem` objects found.

import io
from yamllint.config import YamlLintConfig
from yamllint import linter

yaml_content = """
key: value 
another_key:   with_trailing_spaces
  nested: item
"""

# Use a default configuration or load a custom one
config_string = "extends: default\nrules:\n  trailing-spaces: enable\n  indentation: enable"
conf = YamlLintConfig(content=config_string)

# Lint the YAML content from a string buffer
problems = linter.run(io.StringIO(yaml_content), conf)

found_issues = []
for p in problems:
    found_issues.append(f"Line {p.line}, Column {p.column}: {p.desc} (Rule: {p.rule})")

if found_issues:
    print("YAML linting issues found:")
    for issue in found_issues:
        print(issue)
else:
    print("No YAML linting issues found.")

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