The Problem with the Code-First Workflow

We usually build the backend API first, then wait to build the client after the API is ready. This sequential process often leads to:

• Blocked frontend development – The client team can’t start until the API is finished.
• Misaligned expectations – The API might not meet the frontend’s actual needs.
• More rework – Fixing these mismatches after implementation wastes time and effort.

This approach slows us down and creates friction between teams that should be working in sync.

The API Design-First Solution

The API Design-First approach solves these problems by shifting the API definition phase to the beginning of the project.

Instead of writing code first, we design the API contract collaboratively, with input from frontend, backend, QA, and product stakeholders. This contract defines what the API should look like—its endpoints, requests, responses, and error formats. Once agreed upon, this contract becomes the single source of truth.

How It Can Help Us

Here’s how API Design-First helps us work smarter:

• Frontend and Backend Can Work in Parallel
  Once we define the API contract, we can generate a mock server from it. That means the frontend team can start building immediately—no more waiting on the backend.
• Fewer Surprises, Better Collaboration
  Everyone sees and agrees on the API up front. This means less back-and-forth and fewer misunderstandings during implementation.
• Catch Problems Early
  Design issues (like inconsistent naming, missing fields, or redundant endpoints) are easier to spot before we write a single line of code.
• Clear, Reliable API Specs
  The contract serves as living documentation. No more guessing how an endpoint behaves or relying on outdated Postman collections.
• Automated Testing and Validation
  Tools like Swagger/OpenAPI can validate that our implementation matches the contract. We can even generate tests and documentation from the same source.

Typical Development Flow

Here’s how the API Design-First approach looks in practice:

1. Kickoff and Requirement Gathering
   Stakeholders (product, frontend, backend, QA, etc) meet to discuss API needs and use cases.
2. API Design & Contract Creation
   Use a tool like OpenAPI or Stoplight Studio to define endpoints, request/response formats, status codes, and error structures.
3. Review and Approval
   The contract is reviewed by all parties. Feedback is collected and changes are made until everyone agrees on the spec.
4. Parallel Development Begins
   • Frontend using the API contract we can create a mock server to develop and test UI features.
   • Backend starts implementing the real API according to the contract.
5. Contract-Based Testing
   Automated tests are generated or written to ensure backend responses match the contract.
6. Integration and Final Testing
   Once both sides are implemented, the frontend switches from mock server to the real backend. End-to-end testing is done to validate integration.
7. Contract Maintained as Source of Truth
   Any future changes to the API start with updating the contract and going through the same review process.

What to Watch Out For

Like any approach, API Design-First isn’t without its challenges. Here are a few things we should keep in mind:

• Upfront Investment in Design
  This approach requires more planning and collaboration at the beginning. It may feel slower initially, especially if we’re used to jumping into code right away. But this extra effort pays off by reducing rework later.
• Learning Curve and Tooling Setup
  Tools like OpenAPI, Stoplight, or Swagger UI aren’t difficult, but they do require some learning and setup time. We’ll need to invest a bit to get comfortable and integrate them into our workflow.
• Keeping the Contract in Sync
  Once implementation starts, it’s crucial that the API contract stays up to date. Changes must go through the contract first to avoid drifting from the spec. This requires discipline and possibly updating our development process a bit.
• Not Ideal for Every Tiny Endpoint
  For small internal tools or quick experiments, the overhead of design-first might feel too heavy. It’s best used for projects or APIs that will be maintained, consumed by other teams, or exposed externally.

Despite a few initial hurdles, the benefits far outweigh the costs—especially for services or features where coordination between teams matters.

By recognizing these trade-offs and preparing for them, we can adopt the API Design-First approach more smoothly and get the most out of it.

Final Thoughts

The API Design-First approach aligns perfectly with how modern teams build software: collaboratively, iteratively, and in parallel.
By adopting it, we can:

• ✅ Work faster
  
• ✅ Reduce miscommunication
  
• ✅ Deliver better APIs
  
• ✅ Improve frontend-backend collaboration
  

References

• API-First vs. API Design-First: A Comprehensive Guide
• Understanding the API-First Approach to Building Products