Design a Clear REST API Before Writing Code
Model resources, methods, validation, status codes and error objects before implementing endpoints.
Introduction
An API contract is a promise between a service and its clients. Designing the contract first makes naming, validation and failure behaviour visible before framework code hides the decisions. REST works best when URLs represent stable resources and HTTP methods communicate the intended operation.
How the topic works
Use plural nouns such as /tasks for collections and /tasks/{id} for one resource. GET reads, POST creates, PATCH changes part of a resource and DELETE removes it. Define required fields, types and limits for every request. Choose status codes consistently and return a stable error shape with a machine-readable code and human-readable message.
Practical workflow
- List the resource fields and identify which are server-generated.
- Write routes and methods for list, create, update and delete operations.
- Define request schemas, validation rules and representative responses.
- Specify authentication, authorization, pagination and rate-limit expectations.
- Review the contract with a mock client before implementing handlers.
Tools and technologies
- OpenAPI document
- A diagram or contract table
- An API client for mock requests
Example
POST /tasks accepts a title and optional due date. A valid request returns 201 with the created task and Location header. A missing title returns 400 with {code: "INVALID_TITLE", message: "Title is required"}; a user requesting another user’s task receives 404 or 403 according to the documented security policy.
Common mistakes
- Putting actions such as /createTask in every URL
- Returning 200 for unrelated failures
- Validating shape but not authorization
Security and best practice
Use size limits, server-side validation and least-privilege authorization. Avoid exposing stack traces, database details or whether an inaccessible private record exists.
Portfolio task
Key takeaways
- Resource models come before routes.
- Consistent errors reduce client complexity.
- Authorization is required after validation, not instead of it.