HTTP

Requests, responses, caching and CORS.

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This course has 6 lessons. Start with the first one and use the next / previous links at the bottom of each lesson — the sidebar keeps the whole course in order.

Lessons

HTTP methodsGET, POST, PUT, PATCH and DELETE — what each promises about safety, idempotency, and when to use it.
HTTP status codesThe codes that actually matter in production — and the ones applications routinely get wrong.
HTTP headersContent negotiation, auth, compression and security headers — the metadata that controls real behaviour.
Caching and conditional requestsCache-Control in plain language, ETags versus Last-Modified, and revalidation with 304 responses.
CORS explainedWhy the browser blocks cross-origin reads, how preflight works, and the headers that fix it properly.
HTTPS and TLSWhat TLS actually protects, how certificates get validated, renewal automation, and mixed content traps.

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Last refreshed 2026-09-17.