How Link Validation Works in the Browser
Validating links directly in the browser presents unique challenges and opportunities. The Markdown Link Checker leverages modern web APIs to perform accurate, efficient checks while respecting browser security constraints and user privacy.
When you initiate validation, the tool first parses your Markdown content locally to extract every link—whether inline, reference-style, relative, or anchor. No server involvement occurs at this stage, keeping your content private.
HTTP Request Strategy
For external HTTP and HTTPS links, the application uses the Fetch API to issue lightweight requests. By default, it prefers HEAD requests because they retrieve only headers, reducing bandwidth and speeding up checks. If a HEAD request fails or returns incomplete information, the tool automatically falls back to a GET request for more reliable results.
Each request respects a configurable timeout threshold. If a server does not respond within the set time, the link is marked as unreachable. This prevents slow or unresponsive hosts from hanging the entire validation process.
Handling Redirects
Redirects are common and usually harmless, but they deserve attention. The tool follows redirect chains and reports both the original URL and the final destination, along with the ultimate status code. This transparency helps you decide whether to update links to their canonical form.
Status codes 301, 302, 307, and 308 trigger redirect tracking. The final response determines classification: a successful endpoint marks the link as Redirected but functional, while a broken final destination flags it as Broken.
Status Classification
Links returning codes 200–299 are classified as Valid. Codes 400 and above indicate Broken links. Network errors, CORS restrictions on certain HEAD requests, or timeout failures also result in Broken status with explanatory notes.
Concurrency Control
To avoid overwhelming the browser or triggering rate limits, requests run concurrently with a configurable limit—defaulting to five parallel checks. This balances speed and resource usage, ensuring smooth performance even with hundreds of links.
Relative and Anchor Links
External link validation relies on real network requests, but relative paths and anchors require different handling. The tool supports a virtual file tree feature where you can define project structure, allowing accurate relative resolution. Anchor links are checked against extracted headings in the document itself.
All these operations happen asynchronously in the background, with progress feedback displayed in real time. Once complete, results are presented clearly without any data ever leaving your machine.
This client-side approach delivers fast, private, and reliable link validation tailored to modern browser capabilities.
Understanding the validation process helps you interpret results confidently and maintain healthier documentation.