Luiz H. Rapatão

Luiz H. Rapatão

Staff Software Engineer

2-Minute Read

Contract-First VS Code-First API Documentation

API development is a crucial part of modern software development. Designing clear, robust, and easy-to-use APIs not only optimizes the development process but also enhances the developer experience. Various methodologies exist for API creation, the two significant approaches are the Contract-First and Code-First methods. This article explores these two approaches in depth.

Contract-First API Documentation

Contract-first API development kicks off with the API definition. Developers outline all of the API endpoints, the request-response models, the data types, and any possible status codes. The driving principle here is to write an API contract before any code is written. This contract usually comes in a machine-readable format like Swagger (OpenAPI Spec), RAML, and API Blueprint.

Code-First API Documentation

The code-first approach, as the name suggests, involves writing code before any contractual agreement is established. Developers start building methods, libraries, or classes, and from the implementing codebase, the API documentation is generated.


Both of these techniques have their strengths and weaknesses. Contract-first ensures an agreement and understanding across teams before coding commences, but it can slow things down initially. Code-first gets you into the code quicker but may cause issues down the line if the API design isn’t clearly communicated or understood. As an API developer, your choice between these two approaches should depend on your project’s needs, team communication, and the development workflow.

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