Modern web applications live and die by their APIs. Whether you're building a mobile app, connecting microservices, or creating a platform for third-party developers, your API is the contract that defines how systems communicate.

This section covers everything you need to know to design, implement, and maintain production-grade REST APIs based on web standards and battle-tested patterns.

What You'll Learn #

Each guide in this section takes you from fundamental concepts to advanced implementation details:

Core Topics #

Versioning - How to evolve your API without breaking existing clients
Error Handling - Standardized approaches to communicating failures
Authentication - Securing your API with modern authentication methods
Filtering - Enabling clients to query exactly the data they need
Pagination - Efficiently handling large datasets
Rate Limiting - Protecting your infrastructure from abuse
Content Negotiation - Supporting multiple data formats
Idempotency - Making operations safe to retry
Caching - Leveraging HTTP caching for performance
Observability - Logging, monitoring, and debugging in production

REST Fundamentals #

REST (Representational State Transfer) isn't just a style guide—it's an architectural pattern grounded in the HTTP protocol specification (RFC 7231). Understanding REST means understanding how the web was designed to work.

The Six Constraints #

Roy Fielding's original dissertation defined REST with six architectural constraints:

Client-Server - Separation of concerns between UI and data storage
Stateless - Each request contains all information needed to understand it
Cacheable - Responses must define themselves as cacheable or not
Uniform Interface - Consistent way to interact with resources
Layered System - Client can't tell if connected directly to server
Code on Demand (optional) - Servers can extend client functionality

Getting Started #

If you're new to API design, we recommend starting with these guides in order:

Start with Error Handling to understand how to communicate problems
Move to Authentication to learn about securing your API
Then Versioning to plan for evolution
Finally Caching to make it fast

For specific challenges:

Building a search API? → Read Filtering and Pagination
Payment or transaction API? → Focus on Idempotency
Public API with many users? → Start with Rate Limiting
Need to debug issues? → Jump to Observability

Standards and Specifications #

These guides reference and build upon established web standards:

HTTP/1.1 - RFC 7230-7235 (Protocol fundamentals)
HTTP/2 - RFC 7540 (Performance improvements)
HTTP/3 - RFC 9114 (QUIC-based HTTP)
URI - RFC 3986 (Uniform Resource Identifiers)
JSON - RFC 8259 (JavaScript Object Notation)
OAuth 2.0 - RFC 6749 (Authorization framework)
JWT - RFC 7519 (JSON Web Tokens)
Problem Details - RFC 7807 (HTTP API error responses)

Beyond This Guide #

API design is a vast topic. After mastering these fundamentals, consider exploring:

GraphQL for query flexibility
gRPC for high-performance RPC
WebSockets for real-time bidirectional communication
Server-Sent Events for server-push updates
Webhooks for event-driven integrations

Each has its place, but REST remains the foundation of modern web APIs.