Pure Frontend · Broken Link Detection · Anchor Validation · Duplicate Marking · Reference Check
Zero Dependencies · Works OfflineWhat Can the Markdown Link Checker Do?
The Markdown Link Checker is a pure frontend online tool for extracting and validating all links in Markdown documents. It supports inline links, reference links, image links, auto-links, and heading anchor detection. It automatically validates internal anchors against headings, detects duplicate links and unused reference definitions, and checks external link reachability via browser requests. All parsing is done locally in your browser—no content is ever uploaded to any server.
Core Features
- All Link Type Extraction: Identifies inline [text](url), reference [text][ref], image , auto
, and anchor #heading links - Anchor Validation: Generates heading anchor IDs following GitHub rules and verifies each #anchor link has a matching heading
- Duplicate Link Detection: Flags links pointing to the same URL to help optimize document structure
- Reference Check: Detects reference definitions that are defined but never used, and references that are used but undefined
- External Link Check: Validates external URL reachability via fetch requests (subject to CORS limitations)
How to Use
Step 1: Paste Markdown content in the input box, drag-and-drop a .md file, or click "Load Example".
Step 2: Click "Check Links" or press Ctrl+Enter to automatically extract and validate all links.
Step 3: View results—green for OK, red for issues (broken/missing anchor), yellow for duplicates.
Step 4: Click "Copy Report" or "Download Report" to save results. Ctrl+Shift+C copies instantly.
Use Cases
Documentation Maintenance
Regularly check project READMEs, wikis, and docs for broken links and ensure all external links are still valid and internal anchors are correct.
Pre-Publish Blog Check
Verify all reference links before publishing a blog post to avoid readers hitting 404 pages.
Open Source Contributions
Check documentation links before submitting a PR to avoid CI/CD failures from broken link checks.
Knowledge Base Cleanup
Batch-check knowledge base documents for broken links and clean up stale references.
Technical Background
Markdown link syntax: inline [text](url), reference [text][id] followed by [id]: url, image . GitHub anchor ID generation: lowercase, remove non-alphanumeric chars (keep hyphens and spaces), spaces to hyphens, merge consecutive hyphens. For example, "Hello World!" generates anchor #hello-world. CORS (Cross-Origin Resource Sharing) limits direct browser requests to other domains, so some external links may not be checkable.
FAQ
Which link types can be checked?
Supports inline links [text](url), reference links [text][ref], auto-links
Can it detect external broken links?
External links are checked via fetch requests (subject to CORS limitations). Internal anchors are precisely validated by parsing heading IDs.
Is data uploaded to a server?
No. All Markdown parsing and link extraction is done locally in your browser. External link checks are made directly from the browser.
Does it support drag-and-drop .md files?
Yes. Drag a .md file directly into the input area to load and analyze it.
Can it detect duplicate links?
Yes. The tool flags duplicate links pointing to the same URL and reference link definitions that are defined but never used.
How are anchors validated?
Automatically extracts all headings and generates anchor IDs (following GitHub rules: lowercase, remove special chars, spaces to -), then verifies each #anchor link has a matching heading.
Feedback: dexshuang@google.com