DevTab/Labs

Networking labs

Interactive Networking & Web Labs

Most web bugs hide between the browser and the server: a blocked CORS request, a stale cache, a slow handshake. These labs let you change headers, latency and protocols and watch the exact sequence of messages and decisions.

3 free interactive labs — CORS & Preflight Simulator, HTTP Caching Explained, What Happens When You Type a URL. Each one has an easy-to-hard set of examples, a written explanation and a FAQ, and runs entirely in your browser.

CORS & Preflight Simulator

Edit the request and the server headers, then see exactly why the browser blocks it.

  • When the browser sends a preflight — and when it doesn't
  • Why * and cookies can never be combined
  • How to read and fix the classic CORS console errors
12 minIntermediate9 examplesOpen lab

HTTP Caching Explained

Cache-Control, ETag and 304s, one request at a time.

  • The real difference between no-cache and no-store
  • Why a deploy can stay invisible for hours
  • How reload and hard reload behave differently
12 minIntermediate8 examplesOpen lab

What Happens When You Type a URL

DNS, TCP, TLS and HTTP — with a stopwatch.

  • The full DNS lookup chain, hop by hop
  • Why every new connection costs round trips
  • What TLS 1.3, keep-alive and HTTP/3 actually save
10 minBeginner8 examplesOpen lab

More lab topics

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