# Lint Tool We have a lint tool for catching common mistakes in test files. You can run it manually by running the `wpt lint` command from the root of your local web-platform-tests working directory like this: ``` ./wpt lint ``` The lint tool is also run automatically for every submitted pull request, and reviewers will not merge branches with tests that have lint errors, so you must either [fix all lint errors](#fixing-lint-errors), or you must [add an exception](#updating-the-ignored-files) to suppress the errors. ## Fixing lint errors You must fix any errors the lint tool reports, unless an error is for something essential to a certain test or that for some other exceptional reason shouldn't prevent the test from being merged; in those cases you can [add an exception](#updating-the-ignored-files) to suppress the errors. In all other cases, follow the instructions below to fix all errors reported. ```eval_rst .. wpt-lint-rules:: tools.lint.rules ``` ## Updating the ignored files Normally you must [fix all lint errors](#fixing-lint-errors). But in the unusual case of error reports for things essential to certain tests or that for other exceptional reasons shouldn't prevent a merge of a test, you can update and commit the `lint.ignore` file in the web-platform-tests root directory to suppress errors the lint tool would report for a test file. To add a test file or directory to the list, use the following format: ``` ERROR TYPE:file/name/pattern ``` For example, to ignore all `TRAILING WHITESPACE` errors in the file `example/file.html`, add the following line to the `lint.ignore` file: ``` TRAILING WHITESPACE:example/file.html ``` To ignore errors for an entire directory rather than just one file, use the `*` wildcard. For example, to ignore all `TRAILING WHITESPACE` errors in the `example` directory, add the following line to the `lint.ignore` file: ``` TRAILING WHITESPACE:example/* ``` Similarly, you can also use [shell-style wildcards](https://docs.python.org/library/fnmatch.html) to express other filename patterns or directory-name patterns. Finally, to ignore just one line in a file, use the following format: ``` ERROR TYPE:file/name/pattern:line_number ``` For example, to ignore the `TRAILING WHITESPACE` error for just line 128 of the file `example/file.html`, add the following to the `lint.ignore` file: ``` TRAILING WHITESPACE:example/file.html:128 ```