We rebuilt our product API-first after three years of feature spaghetti. Painful but worth it.

Here’s why API-first matters and how to do it without over-engineering.

What API-First Actually Means

API-first: Design the API before building the UI. The API is the product. The UI is a client.

Not API-first: Build features, add API endpoints later as an afterthought.

The difference matters more than it seems.

Why API-First Works

Internal Consistency

When the API is primary, every feature goes through it. Web app, mobile app, integrations—all use the same API.

Result: Consistent behavior everywhere. Fix a bug once, fixed everywhere.

Our old approach: Web app had features that the API didn’t expose. Mobile was always behind. Integrations were incomplete.

Better Architecture

Designing API-first forces you to think about data structures and relationships clearly.

You can’t hide messy logic behind a UI. The API exposes your thinking.

Future-Proofing

Your UI will change. Your clients will multiply. The API persists.

Good APIs survive complete frontend rewrites. Bad APIs require rewriting everything.

Integration-Ready

Enterprise customers want integrations. Partners want to build on your platform.

API-first means you’re ready. Bolt-on APIs mean you’re scrambling.

When API-First Matters Most

Developer tools: Obviously. Developers are your customers.

B2B SaaS: Integration requirements are high. IT teams want API access.

Platforms: If others build on your product, API is the product.

Mobile + Web: Multiple clients require consistent backend.

When It Matters Less

Simple consumer apps: If you have one client and no integration needs, skip the ceremony.

MVPs for validation: Ship fast. Clean up later.

Non-technical users: They don’t care about your API.

Even then, API-first thinking helps. Just don’t over-engineer.

How to Do API-First Right

Step 1: Design Resources, Not Screens

Think about what your product manages. Users, projects, tasks, whatever.

Design endpoints around resources:

• GET /users
• POST /projects
• PUT /tasks/:id

Not around screens:

• GET /dashboard-data (what even is this?)

Step 2: Document First

Write the API documentation before writing code.

Tools: OpenAPI/Swagger spec, or even plain markdown.

When the docs are clear, implementation is straightforward.

Step 3: Version From Day One

Your API will change. Plan for it.

Simple approach: /api/v1/resource. When breaking changes come, introduce /api/v2/.

Don’t: Break existing integrations without warning.

Step 4: Consistent Conventions

Pick patterns and stick to them:

• Naming: snake_case or camelCase, not both
• Pagination: cursor or offset, consistent approach
• Errors: Standard error response format
• Authentication: One method, well-documented

Inconsistency confuses developers and creates bugs.

Step 5: Build Your UI as a Client

Your frontend should use the same API external developers would use.

This ensures the API is complete and usable.

If your frontend needs special endpoints, ask why. Sometimes valid. Often a sign the API design is incomplete.

The Technology Choices

REST vs. GraphQL

REST: Simpler, more cacheable, better tooling. Use for most cases.

GraphQL: Flexible queries, good for complex data relationships. Use if you need it.

We use REST. GraphQL adds complexity we don’t need.

API Frameworks

Node.js: Express, Fastify, NestJS Python: FastAPI (excellent), Django REST Framework Go: Standard library, Gin, Echo

FastAPI deserves special mention. Auto-generates documentation. Type hints drive validation. Modern Python done right.

Documentation Tools

Swagger/OpenAPI: Industry standard. Auto-generates docs from spec.

Readme.io: Beautiful hosted documentation.

Mintlify: New player, good design.

Good documentation is half the product. Invest in it.

Common Mistakes

Exposing Database Structure

API resources should reflect business concepts, not database tables.

Bad: Returning raw database IDs and internal fields Good: Clean, intentional response structures

Inconsistent Authentication

Pick one auth method. Document it clearly. Don’t make developers guess.

We use API keys for server-to-server, OAuth for user-authenticated requests. Documented clearly.

No Rate Limiting

Without limits, one bad integration can take down your service.

Implement rate limiting from day one. Better to have it and not need it.

Ignoring Errors

Error responses should be as designed as success responses.

Include: Error code, human-readable message, details for debugging.

Not: Generic 500 errors that tell developers nothing.

Our API Checklist

Before launching any API endpoint:

• Documented in OpenAPI spec
• Consistent with existing patterns
• Error responses defined
• Rate limiting in place
• Authentication clear
• Versioned URL
• Example requests in docs

Takes 20 minutes extra per endpoint. Saves hours of support later.

The Business Case

“Why should I care about API quality?”

Developer experience drives adoption. Bad APIs drive developers away.

Integration revenue. API access is often a premium/enterprise feature.

Platform potential. The biggest companies are platforms. APIs enable that.

Reduced support cost. Good APIs mean fewer support tickets.

API-first isn’t just technical preference. It’s business strategy.