API-First Architecture: A Practical Guide
Build your API first, then build everything else on top of it. Here's why this approach produces better software and how to do it right.
API-first architecture means designing and building your API before the frontend, mobile app, or any other consumer. It's a fundamental shift from the traditional approach where the API is an afterthought — bolted onto whatever the backend happens to expose.
This approach produces cleaner architectures, enables parallel development between frontend and backend teams, and creates natural extension points for mobile apps, third-party integrations, and future products you haven't thought of yet.
What API-First Actually Means
API-first doesn't mean you write code before thinking about the user experience. It means you design the contract — the interface between your frontend and backend — before implementing either side. This contract becomes the source of truth that both teams build against.
In practice, this looks like: (1) define your data model and user flows, (2) design the API endpoints that serve those flows, (3) document the API with OpenAPI/Swagger, (4) implement the backend and frontend in parallel, each coding against the agreed contract.
The key insight is that the API contract is a design artifact, not a technical byproduct. It deserves as much thought and iteration as your UI mockups.
REST vs GraphQL vs tRPC
REST is the default and should be your starting point unless you have specific reasons to choose something else. It's widely understood, well-tooled, and simple to cache. Most custom software projects don't need anything more sophisticated.
GraphQL shines when you have many different clients (web, mobile, partner APIs) that each need different slices of the same data. It eliminates over-fetching and under-fetching but adds complexity in caching, error handling, and authorization.
tRPC is excellent when your frontend and backend are both TypeScript. It provides end-to-end type safety without code generation, making API calls feel like local function calls. It's our favorite choice for full-stack TypeScript projects.
REST
Default choice. Simple, cacheable, universally understood. Right for most projects.
GraphQL
Multiple clients needing different data shapes. Worth the complexity only at scale.
tRPC
Full-stack TypeScript. End-to-end type safety without the ceremony of REST or GraphQL.
Authentication and Authorization
Every API needs authentication (who are you?) and authorization (what can you do?). Get these wrong and nothing else matters.
For most projects, JWT tokens with short expiration and refresh tokens provide the right balance of security and developer experience. OAuth 2.0 / OpenID Connect is the standard for third-party authentication. Session-based auth is simpler and still perfectly valid for server-rendered applications.
Authorization should be handled at the API layer, not the frontend. Never trust the client to enforce permissions — the API must validate every request independently.
Versioning and Evolution
APIs evolve. The question isn't whether you'll need to change your API — it's how you'll handle those changes without breaking existing consumers.
URL versioning (/api/v1/, /api/v2/) is the simplest approach and our default recommendation. It's explicit, easy to understand, and simple to route. Header-based versioning is more "correct" but harder to test and debug.
The best strategy is to design your v1 well enough that you rarely need v2. Additive changes (new fields, new endpoints) don't require versioning. Only breaking changes (removing fields, changing semantics) need a version bump.
Frequently Asked Questions
Is API-first only for large projects?
How does API-first work with agile development?
Should we use OpenAPI/Swagger for documentation?
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