The API Design Debate of 2025: Which Side Are You On?

Disclaimer: This post is intended for real human developers – the ones who still write code with their own two hands, haven’t been fully replaced by AI (yet), and still care about API design, developer experience, and scalable architecture.

API First vs Code First: Which One Really Wins? 🚀

First things first: What are we talking about?

When building a software system, especially with microservices or public-facing APIs, there are two common approaches for defining how services communicate:

• Code First: You write your code first (controllers, endpoints, etc.), and generate the API definition (like OpenAPI/Swagger) afterwards.
• API First: You design and define the API contract first (usually in OpenAPI format, a.k.a Swagger), get team alignment, and only then start coding. Typically, teams will generate server-side stubs and client SDKs automatically from the API definition, to ensure consistency and avoid manual errors.

About a decade ago, almost every project I worked on followed one simple approach: Code First – you write the code first, then (maybe) generate the API docs later. If you were lucky, someone would export a Swagger file… if not – good luck reverse-engineering the API from the code 😅.

It made sense back then. When front-end and back-end developers sat in the same room, worked on the same sprint, and could just "talk it out."

But times have changed. Microservices, distributed teams, independent front-end development, external integrations – suddenly API First became more and more critical.

What's the Difference?

Why I’m 100% Team API First

✅ Better planning and design of service contracts

✅ Front-end teams can start early using Mock Servers

✅ Much better control over backward compatibility

✅ Easier API management and Gateway definitions

✅ Reduces the risk of "Oops… we broke something" moments

✅ Automatic code generation for both server-side stubs and client SDKs, keeping everyone aligned and reducing boilerplate coding

✅ The API specification (Swagger/OpenAPI) becomes an integral part of the system design, often written by solution architects or business analysts – even before a single line of code exists

Bottom line: "Design your contract first. Implement later." And please… stop leaving API definitions for the last minute 💥

In Short:

👎 Code First: Quick and dirty. Works for small projects or tightly coupled teams.

👍 API First: The right choice for scalable projects, distributed teams, and modern software development.

What about you?

Which approach does your team use today? Ever gone through the migration from Code First to API First? Would love to hear your thoughts in the comments 👇