Alex Morgan
API Architect
May 15, 2023
12 min read
Well-designed APIs are the backbone of modern software architecture. They enable seamless integration between systems, power mobile applications, and facilitate the development of complex web applications. RESTful APIs, in particular, have become the standard for web service interfaces due to their simplicity, scalability, and alignment with HTTP principles.
This article explores best practices for designing intuitive, efficient, and maintainable RESTful APIs that developers will love to use. Whether you're creating a public API for third-party developers or an internal API for your microservices architecture, these guidelines will help you build interfaces that stand the test of time.
Before diving into specific best practices, it's important to understand the core principles of REST (Representational State Transfer) as defined by Roy Fielding in his doctoral dissertation:
The separation of client and server concerns improves portability across multiple platforms and allows components to evolve independently.
Each request from client to server must contain all the information needed to understand and process the request. The server doesn't store client context between requests.
Responses must define themselves as cacheable or non-cacheable to prevent clients from reusing stale or inappropriate data.
The interface between components is simplified and decoupled, allowing each part to evolve independently. This includes resource identification in requests, resource manipulation through representations, self-descriptive messages, and hypermedia as the engine of application state (HATEOAS).
A client cannot ordinarily tell whether it is connected directly to the end server or to an intermediary along the way, allowing for load balancing, shared caches, and security policies.
Servers can temporarily extend client functionality by transferring executable code, such as JavaScript, to the client.
Resources should be named using nouns that represent the entities in your domain model, not verbs that represent actions on those entities.
Good:
/users/products/ordersAvoid:
/getUsers/createProduct/updateOrderCollections should use plural nouns to clearly indicate that they represent multiple items.
Good:
/users (collection)/users/123 (specific item)Avoid mixing singular and plural:
/user and /users/123Nested resources can effectively represent containment relationships between entities.
Examples:
/users/123/orders (all orders for user 123)/users/123/orders/456 (order 456 for user 123)However, avoid nesting resources too deeply (more than 2-3 levels) as it can make URLs unwieldy and complicate client implementation.
Query parameters should be used for operations that don't fundamentally change the nature of the resource being requested.
Examples:
/products?category=electronics (filtering)/products?sort=price_asc (sorting)/products?limit=10&offset=20 (pagination)Each HTTP method has specific semantics that should be respected:
Idempotent methods (GET, PUT, DELETE) should produce the same result regardless of how many times they are called, improving reliability in distributed systems.
For example, sending the same PUT request multiple times should result in the same state, not create multiple resources or cause cumulative effects.
HTTP status codes provide valuable information about the result of a request. Use them consistently and appropriately:
Success codes:
Client error codes:
Server error codes:
JSON has become the de facto standard for API responses due to its simplicity, readability, and widespread support across programming languages.
Include the Content-Type: application/json header in responses, and parse the Accept header from requests to support content negotiation if needed.
Maintain a consistent structure for all API responses to make client-side parsing predictable:
{
"data": {
// Resource or collection data
},
"meta": {
"pagination": {
"total": 100,
"count": 10,
"per_page": 10,
"current_page": 1,
"total_pages": 10
}
},
"links": {
"self": "https://api.example.com/products?page=1",
"next": "https://api.example.com/products?page=2",
"prev": null
}
}Error responses should provide enough information for developers to understand and fix the issue:
{
"error": {
"code": "validation_error",
"message": "The request contains invalid parameters",
"details": [
{
"field": "email",
"message": "Must be a valid email address"
},
{
"field": "password",
"message": "Must be at least 8 characters long"
}
]
}
}Allow clients to request only the fields they need, reducing response size and improving performance:
/users?fields=id,name,email
Always paginate collection responses to prevent performance issues with large datasets. Include metadata about the pagination state and links to navigate between pages:
Common pagination approaches:
/products?limit=10&offset=20/products?page=2&per_page=10/products?after=abc123&limit=10 (better for large datasets)Even if you're on version 1, implement versioning from the start to establish patterns for future changes.
Common versioning approaches:
/v1/products/products?version=1Accept: application/vnd.example.v1+jsonURL path versioning is the most straightforward and visible approach, though header-based versioning offers more flexibility.
When incrementing version numbers, follow these guidelines:
When evolving your API, provide clear timelines and migration paths for deprecated features:
Always use HTTPS to encrypt data in transit, protecting sensitive information and preventing man-in-the-middle attacks.
Choose an authentication mechanism appropriate for your API's context:
Protect your API from abuse and ensure fair usage by implementing rate limiting:
X-RateLimit-Limit: Total allowed requests in a periodX-RateLimit-Remaining: Requests remaining in the current periodX-RateLimit-Reset: Time when the limit resetsNever trust client input. Implement thorough validation for all request parameters, headers, and body content to prevent injection attacks and data corruption.
Good documentation is essential for API adoption and proper usage:
The OpenAPI Specification provides a standardized format for API documentation that can be used to generate interactive documentation, client libraries, and server stubs.
For widely-used programming languages, consider providing official client libraries to simplify integration and promote best practices.
For public APIs, a developer portal can significantly improve the developer experience by providing:
Use HTTP caching mechanisms to reduce server load and improve response times:
Cache-Control headersEnable GZIP or Brotli compression for API responses to reduce bandwidth usage and improve performance, especially for mobile clients.
For large datasets, cursor-based pagination generally performs better than offset-based pagination, especially as users navigate to later pages.
For operations that take significant time to complete, implement asynchronous processing:
The GitHub API is widely regarded as a well-designed RESTful API that exemplifies many of the best practices discussed in this article:
/users/{username}/reposBy studying the GitHub API design, developers can gain insights into practical implementations of RESTful principles at scale.
Designing a great RESTful API requires careful consideration of resource modeling, HTTP semantics, response formats, versioning strategies, security measures, and developer experience. By following the best practices outlined in this article, you can create APIs that are intuitive to use, perform well at scale, and evolve gracefully over time.
Remember that API design is both an art and a science. While these guidelines provide a solid foundation, always consider your specific use cases and user needs when making design decisions. The ultimate measure of a successful API is how effectively it serves the developers who use it.
Explore the latest approaches to web architecture that prioritize performance, scalability, and maintainability in today's complex digital landscape.
A comparative analysis of modern frontend frameworks and how to select the best one for your project.
How serverless computing is changing web development and when it makes sense for your projects.