HTTP & The Web
How browsers and servers talk: requests and responses, status codes, headers, redirects and soft 404s.
Beginner
3 guidesHTTP status codes: what each one means and what to do
HTTP status codes by class, from 200 and 301 to 404, 429 and 503. Each entry says what the code means and what to do when you see it.
What is a redirect? Server, meta refresh and JavaScript
A redirect sends a browser or crawler from one URL to another. How 3xx, meta refresh and JavaScript redirects work, when to use each and what they cost.
301 vs 302 redirects: which to use, plus 307 and 308
A 301 is a permanent redirect and a 302 a temporary one. How 307 and 308 differ, how browsers cache each code and how search engines read them.
Intermediate
4 guidesHTTP request anatomy: request line, headers and body
What each part of an HTTP request does: the request line, the headers that matter most, the body, and which methods are safe or idempotent.
HTTP response anatomy: status line, headers and body
How to read an HTTP response: the status line, headers such as Content-Type, Cache-Control, ETag and Set-Cookie, the body, and raw headers with curl.
Redirect chains and loops: how to find and fix them
A redirect chain is two or more redirects in a row before the final page. What causes chains and loops, what they cost, and how to find and flatten them.
Soft 404 errors: what they are and how to fix them
A soft 404 is a missing page that returns 200 OK instead of 404. What causes them, how to detect them with curl and Search Console, and how to fix them.
Tools for this topic
Try what these guides describe on your own URLs, domains, code or files.
Paste a request copied as cURL from browser dev tools and get code for 16 libraries, with headers and body carried over.
Sign in to review the security headers and cookie flags a URL returns, and what each one does in practice.
Check the final status code, every redirect hop and response time for a list of URLs, then export the results as CSV or JSON.