Netcheck Gets an Ookla Speedtest Server, DNS Probing & More

I put Netcheck together a few months ago for a specific problem: I wanted to know whether my ISP was throttling a certain connection. One thing led to another, and now it runs speed tests, probes DNS resolvers, and scores ad blockers.

What’s new

Ookla Speedtest: city-aware server discovery via Ookla’s API, CORS-safe direct download/upload, and a service worker that bypasses no-store caching for accurate measurements.

DNS wire-format probing: probes resolvers directly over the DNS wire format instead of relying on system APIs. It catches resolvers that lie about:

• Recursion path probing: which upstream resolvers are actually handling your queries
• ECS (EDNS Client Subnet) leaks: whether your resolver is leaking your approximate location to authoritative nameservers
• Real DNSSEC validation: not only whether the resolver claims to support DNSSEC, but also whether it actually validates

Ad-block scoring: weighted by category importance instead of a flat count, so blocking tracking networks counts more than blocking generic ad domains.

Service worker fixes: the speedtest now works reliably even when the browser’s Cache-Control headers say no-store, and the worker cache-busts Ookla URLs to prevent stale measurements.

Check it out at netcheck.oilygold.xyz. Source on GitHub.