# Internal link checking tool
You can use [htmltest](https://github.com/wjdp/htmltest) to check for broken links in [`/content/en/`](https://git.k8s.io/website/content/en/). This is useful when refactoring sections of content, moving pages around, or renaming files or page headers.
## How the tool works
`htmltest` scans links in the generated HTML files of the kubernetes website repository. It runs using a `make` command which does the following:
- Builds the site and generates output HTML in the `/public` directory of your local `kubernetes/website` repository
- Pulls the `wdjp/htmltest` Docker image
- Mounts your local `kubernetes/website` repository to the Docker image
- Scans the files generated in the `/public` directory and provides command line output when it encounters broken internal links
## What it does and doesn't check
The link checker scans generated HTML files, not raw Markdown. The htmltest tool depends on a configuration file, [`.htmltest.yml`](https://git.k8s.io/website/.htmltest.yml), to determine which content to examine.
The link checker scans the following:
- All content generated from Markdown in [`/content/en/docs`](https://git.k8s.io/website/content/en/docs/) directory, excluding:
- Generated API references, for example https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.18/
- All internal links, excluding:
- Empty hashes (`` or `[title](#)`) and empty hrefs (`` or `[title]()`)
- Internal links to images and other media files
The link checker does not scan the following:
- Links included in the top and side nav bars, footer links, or links in a page's `` section, such as links to CSS stylesheets, scripts, and meta information
- Top level pages and their children, for example: `/training`, `/community`, `/case-studies/adidas`
- Blog posts
- API Reference documentation, for example: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.18/
- Localizations
## Prerequisites and installation
You must install
* [Docker](https://docs.docker.com/get-docker/)
* [make](https://www.gnu.org/software/make/)
## Running the link checker
To run the link checker:
1. Navigate to the root directory of your local `kubernetes/website` repository.
2. Run the following command:
```
make docker-internal-linkcheck
```
## Understanding the output
If the link checker finds broken links, the output is similar to the following:
```
tasks/access-kubernetes-api/custom-resources/index.html
hash does not exist --- tasks/access-kubernetes-api/custom-resources/index.html --> #preserving-unknown-fields
hash does not exist --- tasks/access-kubernetes-api/custom-resources/index.html --> #preserving-unknown-fields
```
This is one set of broken links. The log adds an output for each page with broken links.
In this output, the file with broken links is `tasks/access-kubernetes-api/custom-resources.md`.
The tool gives a reason: `hash does not exist`. In most cases, you can ignore this.
The target URL is `#preserving-unknown-fields`.
One way to fix this is to:
1. Navigate to the Markdown file with a broken link.
2. Using a text editor, do a full-text search (usually Ctrl+F or Command+F) for the broken link's URL, `#preserving-unknown-fields`.
3. Fix the link. For a broken page hash (or _anchor_) link, check whether the topic was renamed or removed.
Run htmltest to verify that broken links are fixed.