HTTP Semantics
This is the core contract of every web API, browser request, and server response. You can't design or debug HTTP without knowing this.
What It Defines
The foundational HTTP spec. Defines methods (GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS), status codes (1xx-5xx), headers, content negotiation, conditional requests, range requests, and the https URI scheme.
Canonical (Normative)
Convenient (Practical)
Related References
The canonical publication point for finalized RFCs. If a protocol is standardized as an RFC, the RFC Editor text is the normative final reference. Published by the IETF, IRTF, IAB, and independent stream.
Related Specs
Correct caching is the difference between a fast app and an expensive, slow one. Mis-configured cache headers cause stale data bugs and unnecessary origin load.
HTTP/1.1 is still the baseline. Load balancers, proxies, and debugging tools often present HTTP in this format. Understanding the wire format is essential.
HTTP/3 is the current performance frontier for web delivery. CDNs enable it automatically; understand it for performance tuning and debugging.
Every HTTPS connection, SMTP/IMAP over TLS, OAuth token exchange, and API call uses TLS. It is the foundational security layer.
If you're returning 402 — or shopping for a way to monetize an API or MCP server — the spec hands you the code and nothing else. The meaning lives entirely in whatever protocol you layer above it: x402 (stablecoins, X-PAYMENT header), L402 (Lightning, WWW-Authenticate macaroon+invoice), or your own. Knowing that 402 itself is a blank canvas is the difference between shipping an interoperable agent-payable endpoint and a 402 response no client can negotiate against.
x402 is the leading candidate for the agent-economy payment rail: it lets an AI agent (or any HTTP client) pay for an API call inline, with no API key, no signup, and no human-in-the-loop. If you're building agentic apps, paid MCP servers, per-request data products, or anything where "charge for this request without a session" matters, x402 is the standard to know — supported by Coinbase, Cloudflare, Vercel AI Gateway, and a growing facilitator ecosystem.