What is API-first design?
API-first means designing your application's API before building the frontend. Instead of building a UI and then figuring out what data it needs, you define the contract between your frontend and backend upfront.
This sounds like a small change in order of operations, but it fundamentally changes how software gets built.
Why it matters
When you build the UI first, the API becomes an afterthought. It ends up tightly coupled to one specific frontend, full of inconsistencies, and painful to extend. Every new feature requires changes on both sides.
With API-first design:
- Frontend and backend teams can work in parallel. Once the API contract is agreed, both sides build independently.
- Your API becomes reusable. The same API serves your web app, mobile app, third-party integrations, and internal tools.
- Testing is simpler. You can test the API in isolation before any UI exists.
- Documentation comes free. If you design the API first, the spec is the documentation.
How we do it at stackForm
Every project starts with an API design phase. Here's our process:
1. Define the resources
What are the core objects in your system? Users, orders, invoices, projects? List them out and define their relationships.
2. Design the endpoints
For each resource, define the operations: create, read, update, delete, list. Use RESTful conventions or GraphQL schemas depending on the project.
GET /api/projects
POST /api/projects
GET /api/projects/:id
PATCH /api/projects/:id
DELETE /api/projects/:id
3. Write the spec
We use OpenAPI (Swagger) for REST APIs. The spec defines every endpoint, request body, response shape, and error code. This becomes the single source of truth.
4. Mock it
Before writing any backend code, we generate a mock server from the spec. The frontend team can start building immediately against realistic fake data.
5. Build and validate
Backend implements the real API against the spec. Automated tests validate that the implementation matches the contract. If the tests pass, the frontend works without changes.
When to use it
API-first is ideal for:
- Apps with multiple clients (web + mobile)
- Products that will need third-party integrations
- Teams with separate frontend and backend developers
- Any project where the API might outlive the current UI
For a simple marketing site or internal tool with one developer, it's overkill. But for anything with complexity or longevity, it pays for itself quickly.
The bottom line
Your API is the foundation of your product. Treat it like a first-class citizen, not a side effect of your UI. Design it first, document it properly, and everything built on top of it will be better for it.