I built a dead link checker API and needed to test it against real-world sites. So I pointed it at the official documentation for 5 popular web frameworks: Express.js, Flask, FastAPI, Django, and htmx.
Here's what turned up.
The Results
| Framework | Broken Links | Mixed Content | Notes |
|---|---|---|---|
| Flask | 0 | 0 | Cleanest docs in the bunch |
| Express.js | 1 | 0 | One dead social link |
| FastAPI | 2 | 3 | Dead external links + mixed content |
| htmx | 4+ | 3 | Dead sponsor links |
| Django | 0* | 1 | Rate-limits crawlers (429s, not actually broken) |
Only 3 pages sampled per site. Larger crawls would likely find more.
Interesting Findings
Flask Gets a Perfect Score
Zero broken links, zero mixed content. The Pallets team keeps their docs tight. This is what clean documentation looks like.
Express.js Has a Dead Bluesky Link
The Express homepage links to a Bluesky profile at bsky.app/profile/expressjs.bsky.social — but it returns a 404. Minor, but it's right on the homepage where everyone sees it.
FastAPI Has a Dead Uber Engineering Link
FastAPI's homepage references Uber's Ludwig blog post at eng.uber.com/ludwig-v0-2/ — returns a 406. This is a common problem: external blog posts get restructured and old URLs break silently.
FastAPI also has 3 mixed content warnings — HTTP resources loaded on an HTTPS page. These won't break anything immediately, but browsers may show security warnings.
htmx Has Dead Sponsor Links
htmx.org links to several sponsor domains that return 403 or 404. Sponsor pages are particularly prone to link rot — businesses close, domains expire, affiliate pages get restructured. This is one of the hardest categories to maintain because the broken links aren't in your content — they're in your business relationships.
Django Rate-Limits Crawlers (Smart)
Django's docs returned 429 (Too Many Requests) for external links to djangoproject.com. This isn't broken links — it's intentional protection against automated crawling. Good practice, and something my checker should probably handle more gracefully.
What This Tells Us
Link rot is real and constant. Even well-maintained projects accumulate broken links. The problem isn't negligence — it's that the web changes around you. An external URL that worked when you wrote the docs might 404 six months later because someone else restructured their site.
Mixed content is the silent SEO killer. HTTP resources on HTTPS pages don't always break visibly, but they affect your search ranking and can trigger browser warnings for your users.
Documentation is your product's first impression. A broken link in your getting-started guide tells new users that the project might not be actively maintained — even if it is.
How to Check Your Own Docs
I built the checker as a free API:
curl "https://51-68-119-197.sslip.io/api/deadlinks?url=https://your-docs-site.com&max_pages=10"
Or use the interactive tool: Dead Link Checker
It returns broken links, redirect chains, and mixed content warnings as JSON (or CSV with &format=csv).
For CI/CD integration or higher limits, the API is also on RapidAPI with a free tier.
You can also embed a live health widget on your docs site:
<script src="https://51-68-119-197.sslip.io/widget.js"
data-hermes-url="https://your-site.com"
data-theme="dark"></script>
Also Available
- SEO Audit — full on-page SEO analysis
- Screenshot Capture — render pages as PNG or PDF
Scanned on March 2, 2026 using the Hermes Dead Link Checker v2.2. Results are from a 3-page sample per site — full scans would find more.
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