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Document Link ValidatorDetects 404 Broken In-Page Anchors

Markdown Internal Anchor Checker

Validate all internal anchor links (`#section-name`) across your Markdown document against actual headings. Catch broken table-of-contents links before publishing to GitHub.

3 Valid Anchors2 Broken Anchors
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Markdown Source Document
Input: 621 characters5 total in-page anchors
Anchor Validation AuditGitHub-compliant Slug Matching

Broken Anchors (2)

Broken Link Example
Target: #non-existent-section
Line 8
API Reference
Target: #api-documentation
Line 9

Valid Verified Anchors (3)

Getting Started
#getting-started
Line 6
System Architecture
#system-architecture
Line 7
Contributing Guidelines
#contributing
Line 10
Instant GitHub Slug Audit100% In-Browser
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Complete Guide & Overview

Check & Fix Broken Internal Anchor Links in Markdown Online

Verify that internal anchor links ([Section](#section-name)) point to real headings in your document. Identifies broken table-of-contents links and reports line numbers for instant fixing.

How to Use the Markdown Anchor Checker

1

Paste Markdown

Input your documentation page or README containing table of contents links.

2

Instant Verification

The validator matches every in-page anchor (#slug) against all document headings.

3

Fix Broken Headings

Review reported broken anchors and line numbers to correct typos or missing sections.

Key Features & Capabilities

GitHub Slug Matching: Accurately computes CommonMark URL anchor slugs from heading titles.
Pinpoint Line Numbers: Identifies the exact line number of every broken anchor reference.
Visual Distinction: Displays broken links with red alert tags and verified links in green.
Code Block Safe: Ignores comments and hashtags inside code fences.
100% In-Browser Privacy: Safely audit internal technical wikis and documentation drafts.

Pro Tips & Best Practices

  • •Run this checker before submitting large open source documentation PRs to guarantee zero dead jumps in your table of contents.

Frequently Asked Questions

Why do internal anchor links break in Markdown?

When an author renames a heading (e.g. from '## Quick Start' to '## Installation'), earlier table of contents links pointing to '#quick-start' stop working, leaving users with dead clicks.

How does GitHub generate anchor slugs?

GitHub converts heading titles to lowercase, removes punctuation (dots, commas, parentheses), and replaces whitespace with hyphens.

Does this tool audit external website links?

This tool specifically focuses on internal document anchors (#slug). To audit external HTTP/HTTPS links and images, use our companion tool 'Markdown Link Extractor'.

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