Using the content linter

About the GitHub Docs content linter

Our content linter enforces style guide rules in our Markdown content.

The linter uses markdownlint as the framework to perform checks, report flaws, and automatically fix content, when possible. This framework flexibly runs specific rules, gives descriptive error messages, and fixes errors. The GitHub Docs content linter uses several existing markdownlint rules and additional custom rules to check the Markdown content in our content and data directories. Our custom rules implement checks that are either not yet available in the markdownlint framework or are specific to GitHub Docs content. Rules check the syntax for both Markdown and Liquid.

Running the GitHub Docs content linter

The GitHub Docs content linter will run automatically on pre-commit, but you can also run it manually.

Automatically run the linter on pre-commit

When you are writing content locally and committing files using the command line, those staged files will automatically be linted by the content linter. Both warnings and errors are reported, but only errors will prevent your commit from completing.

If any errors are reported, your commit will not complete. You will need to fix the reported errors, re-add the changed files, and commit your changes again. Any errors that are reported must be fixed to prevent introducing errors in the content that are in violation of the GitHub Docs style guide. If any warnings are reported, you can optionally choose to fix them or not.

When you are writing content locally, there are several rules that you can fix automatically using the command line. If you want to automatically fix errors that can be fixed, see "Automatically fix errors that can be fixed."

If you are editing a file in the GitHub UI, you will not be able to automatically fix errors or run the linter on a commit, but you will get a CI failure if the content violates any rules with a severity of error.

Manually run the linter

Run the linter on staged and changed files

Use the following command to run the linter locally on your staged and changed files. It will output both warning and error severity flaws.

npm run lint-content

Run the linter on staged and changed files and only report errors

Use the following command to run the linter locally on your staged and changed files, and report only error severity flaws.

npm run lint-content -- --errors

Run the linter on specific files or directories

Use the following command to run the linter locally on specific files or directories. Separate multiple paths with a space. You can include both files and directories in the same command.

npm run lint-content -- \
  --paths content/FILENAME.md content/DIRECTORY

npm run lint-content -- \
  --paths content/FILENAME.md content/DIRECTORY

Automatically fix errors that can be fixed

If an error has fixable: true in its description, you can use the following commands to automatically fix them.

Run this command to fix staged and changed files only:

npm run lint-content -- --fix

Run this command to fix specific files or directories:

npm run lint-content -- \
  --fix --paths content/FILENAME.md content/DIRECTORY

Run a specific set of linter rules

Use the following command to run one or more specific linter rules. These examples run the heading-increment and code-fence-line-length rules. Replace heading-increment code-fence-line-length with one or more linter aliases that you would like to run. To see the list of linter rules you can pass to this option, run npm run lint-content -- --help. You can use either the short name (for example, MD001) or long name (for example, heading-increment) of a linter rule.

Run the specified linter rules on all staged and changed files:

npm run lint-content -- \
  --rules heading-increment code-fence-line-length

Run the specified linter rules on specific files or directories:

npm run lint-content -- \
  --rules heading-increment code-fence-line-length \
  --path content/FILENAME.md content/DIRECTORY

Bypass the commit hook

If the linter catches errors that you did not introduce, you can bypass the git commit hook by using the --no-verify option when you commit your changes.

git commit -m 'MESSAGE' --no-verify

Display the help menu for the content linter script

npm run lint-content -- --help

Linting rules

Each rule is configured in a file in src/content-linter/style, which is where the severities of rules are defined.

Errors must be addressed before merging your changes to the main branch. Warnings should be addressed but do not prevent a change from being merged into the main branch. Most rules will eventually be promoted to errors, once the content no longer has warning violations.

Syntax for linting rules

Some linting rules return warnings or errors based on HTML comments that you can add to articles.

Syntax for expiring and expired content

Rules GHD038 and GHD039 check for content that has been manually given an expiration date. Fourteen days before the specified date, the content linter will return a warning that the content is expiring soon. Starting on the specified date, the content linter will return an error and flag the content for remediation.

You can add an expiration date to content by wrapping it in HTML tags that contain an expiration date in the format: <!-- expires yyyy-mm-dd --> <!-- end expires yyyy-mm-dd -->

Use:

This content does not expire.
<!-- expires 2022-01-28 -->
This content expires on January 28, 2022.
<!-- end expires 2022-01-28 -->
This content also does not expire.

Note, if you are placing the expired tags in an HTML table element, make sure the tag goes around the entire row and not just the cell. For example:

<!-- expires 2024-06-28 -->
<tr>
<td>
macOS
</td>
<td>
The <code>macos-11</code> label is closing down and will no longer be available after 28 June 2024.
</td>
</tr>
<!-- end expires 2024-06-28 -->

Suppressing linter rules

Rarely, you may need to document something that violates one or more linter rules. In these cases, you can suppress rules by adding a comment to the Markdown file. You can disable all rules or specific rules. Always try to limit as few rules as possible. You can disable a rule for an entire file, for a section of a Markdown file, a specific line, or the next line.

For example, if you are writing an article that includes the regular expression (^|/)[Cc]+odespace/ that checks for reversed link syntax, it will trigger the MD011 rule that checks for reversed links. You can disable the rule MD011 on that specific line by adding the following comment.

(^|/)[Cc]+odespace/ <!-- markdownlint-disable-line MD011 -->

If the line you're trying to ignore is in a code block, you can ignore the code block by surrounding it with the following comments.

<!-- markdownlint-disable MD011 -->
```
(^|/)[Cc]+odespace/
```
<!-- markdownlint-enable MD011 -->

You can use these comments to enable or disable rules.