Checking Anchor Links (Fragment Identifiers)

lychee can check anchor links (also called fragments) in both HTML and Markdown files. This feature helps ensure that internal links to specific sections of a page are valid.

Quick Start

To enable anchor link checking, use the --include-fragments flag:

lychee --include-fragments 'https://example.com/docs'

Supported Formats Overview

Feature	Markdown	HTML	Inline HTML in Markdown
Heading-based fragments	✅	✅	✅
Custom ID fragments	✅	✅	✅
Unicode in fragments	✅	✅	✅
Inline code in headings	✅	N/A	N/A

Detailed Information

Supported Formats

• Markdown (.md) files
• HTML (.html) files
• Inline HTML within Markdown files

Supported Anchor Link Types

• Links to headings (e.g., #introduction)
• Links to custom IDs (e.g., #custom-section-id)
• Unicode characters in fragments (e.g., #résumé)

How does lychee generate fragments for comparison?

lychee uses two main methods:

1. Heading Attributes: For explicit IDs specified in Markdown (e.g., ## My Heading {#custom-id})
2. Unique Kebab Case: For standard headings, similar to GitHub’s auto-generated anchors

Supported Edge Cases

lychee handles:

• Headings with inline code (e.g., # `code` in heading)
• Unicode characters in headings
• Underscores in headings (preserved in fragments)

Limitations

• Complex or nested HTML structures might not be fully supported
• JavaScript-generated anchors cannot be checked
• Some advanced Markdown or HTML processor-specific features may not be recognized. Create an issue if you encounter any problems.

Troubleshooting

In case of issues with anchor link checking, here are some tips:

• Use explicit IDs for complex headings or when targeting specific elements
• Ensure your Markdown and HTML follow standard practices for heading structures
• For HTML files, use the id attribute on elements you want to link to