API stands for Application Programming Interface. REST stands for Representational State Transfer. So API REST refers to a RESTful API, which is an API that follows the principles and constraints of REST architectural style.
What is an API?
An API (Application Programming Interface) is a set of protocols, routines, functions and tools that enable software applications to communicate with each other. APIs provide a standardized way for one piece of software to access data and features of another software application. This allows developers to abstract away low level implementation details and access higher level functionality in a simple, consistent way.
For example, the Twitter API allows other programs to access user profiles, read tweets, post new tweets, and more. The Google Maps API allows developers to embed Google Maps and add markers, directions and other mapping features to their own sites and apps. APIs are important because they simplify work for developers and expand what’s possible by letting applications work together.
What is REST?
REST stands for Representational State Transfer. It is an architectural style for building distributed systems based on hypermedia APIs. The term was coined in 2000 by Roy Fielding in his doctoral dissertation. REST aims to leverage existing HTTP protocol features and infrastructure to create scalable web services.
Some key principles of REST APIs include:
- Client-Server – Separation of concerns between UI and data storage
- Stateless – No client session state stored on server, each request has full context
- Cacheable – Responses indicate if they can be cached to improve performance
- Uniform Interface – Resources exposed at endpoints, manipulated via standard HTTP methods
- Layered System – Intermediary servers can improve scalability, security, performance
By leveraging HTTP’s existing features, REST aims to create loose coupling between client and server. This improves scalability and allows components to evolve independently. REST has become a de facto standard for building APIs used in modern web and mobile apps.
What is an API REST?
An API REST (or RESTful API) follows the design principles and constraints of the REST architectural style. This means:
- Resources are uniquely addressed using URIs
- Standard HTTP methods like GET, POST, PUT, DELETE are used to manipulate resources
- Messages are self-descriptive containing resource representation formats like JSON
- Stateless client-server communication with no saved session state on server
Some other common features of REST APIs:
- Structured use of HTTP response codes to indicate errors, validation issues, etc.
- Authentication handled via tokens, API keys, OAuth etc. not sessions
- Clearly defined hierarchy of resources through URI namespace
- Hypermedia links for discovery and navigation between resources
- Responses contain enough metadata for client to assemble next request
By strictly adhering to REST constraints, an API gains desirable non-functional features like loose coupling, scalability and cacheability essentially “for free”. This has helped drive wide adoption of API REST.
REST API Examples
Here are some examples of popular REST APIs:
- Twitter – The Twitter REST API allows developers access to public Twitter data. API endpoints exist for timelines, tweets, users, direct messages, friendships, media, search and more.
- GitHub – GitHub’s API provides RESTful access to Git repositories, user profiles, organizations, issues, pull requests and more GitHub entities and features.
- Stripe – Stripe’s API enables access to perform operations on payments, refunds, invoices, customers and more. Flexible authentication and webhooks provided.
- Twilio – Twilio’s REST API allows sending/receiving voice calls, SMS messages and video calls. API also provides access to Twilio client, chat and taskrouter services.
- Google Maps – The Google Maps API provides REST access to maps, routes, places, geocoding/reverse geocoding, distance matrix calculations, roads and more mapping data.
Benefits of REST APIs
There are many benefits to the REST approach for building APIs. Some key ones include:
- Scalability – Stateless client-server allows for scaling servers horizontally
- Reliability – REST leverages HTTP which is reliable and resilient
- Performance – Cacheable responses speed up repeat requests
- Simplicity – Uniform interface with self-descriptive messages
- Portability – Use any language, platform, frameworks that support HTTP
- Layered System – Intermediaries like caches improve performance
- Separation of Concerns – Decoupled client/server enables independent evolution
- Visibility – REST uses open standards so services are visible
The REST principles and constraints aim to create APIs optimized for use over the web. Adhering to the REST architectural style has helped countless APIs achieve massive scale, reliability and portability across platforms.
Challenges with REST APIs
While REST APIs have many benefits, some challenges exist as well:
- Over-fetching – Clients often retrieve more data than needed
- Chatty interfaces – Many small synchronous requests impact performance
- Versioning – No standards for dealing with changes over time
- Hypermedia – Links for discovery rarely well supported
- Documentation – OpenAPI standard helps, but still a challenge
- Non-standard status codes – Overuse of 2xx status codes even for errors
While many challenges exist, continued evolution of API practices, tools, frameworks and standards helps address these. For example, GraphQL and OpenAPI help address some REST API drawbacks.
REST vs SOAP APIs
SOAP is another style of web service API that uses XML for messaging and follows a rigid contract-first approach. Compared to SOAP, key differences with REST APIs include:
| REST | SOAP |
|---|---|
| Lightweight, uses HTTP | Heavier protocol, usually HTTP + XML |
| Stateless, no server session state | Can maintain session state |
| Use common HTTP methods | Defines own methods in contract |
| Human-readable responses like JSON | XML for messaging |
| No strict contract | Rigid contract-first approach |
Overall REST aims to leverage simplicity and features of HTTP while SOAP is much more complex but offers more process rigor. In recent years REST has become much more popular for public web APIs while SOAP remains common in enterprise use cases.
REST API Design Tips
Here are some best practices for effective API REST design:
- Keep URLs and payloads as simple and intuitive as possible
- Use nouns to represent resources, verbs for operations
- Pluralize collection resource names
- Keep verbs consistent for a resource (GET, POST, PUT, DELETE)
- Use HTTP status codes to indicate all request outcomes
- Validate all input and output data
- Support common request parameters like limit, offset, filter
- Include links for discovery in payload when possible
- Provide thorough documentation and examples
Careful planning of URL structure, request methods, status codes and representations will go a long way in creating intuitive, scalable APIs.
REST API Security
Some options for securing REST APIs include:
- HTTPS – Encrypt API traffic in transit end-to-end
- Authentication – Validate identity via API keys, OAuth etc
- Access Control – Restrict access with allow lists, permissions etc
- Rate Limiting – Block or throttle excessive requests
- Validation – Sanitize all input data
- Security Scanning – Scan deployed API for vulnerabilities
A layered approach should be taken, building security into the API design from the start and adding protections in transit, on the edge and at the application layers.
Testing REST APIs
Strategies for testing REST APIs include:
- Unit testing – Isolate and test individual methods and classes
- Integration testing – Verify API works end-to-end as expected
- Functional testing – Test key user workflows and acceptance criteria
- Load testing – Stress test API under production-like loads
- Security testing – Probe for vulnerabilities like injections
- Automated testing – Script tests to run on every code change
A combination of manual and automated testing during development and in production helps surface issues and validate availability, performance, security and functionality of the API.
Popular REST API Frameworks
Some widely used frameworks for building REST APIs include:
- Express – Fast, minimalist Node.js framework
- Flask – Python microframework for building web services
- Django REST Framework – Powerful Python toolkit for APIs
- Spring – Robust Java framework with REST support
- Ruby on Rails – RESTful APIs easily built with Rails
- ASP.NET Core – Microsoft’s cross-platform framework
These provide helpers, boilerplate code and structures to simplify building RESTful web APIs in various languages and environments.
The Future of REST APIs
While REST APIs are mature and widely adopted, new technologies are emerging as potential successors with their own strengths and weaknesses including:
- GraphQL – Query language for APIs focused on performance
- gRPC – Google’s high-performance remote procedure call protocol
- WebSockets – Enable real-time bidirectional communication
- HTTP/2 – Improves HTTP request multiplexing and more
REST will likely remain popular for public APIs but may gradually get replaced internally by GraphQL, gRPC and other protocols optimized for microservices. The API landscape will continue rapidly evolving to power smarter, faster, more scalable systems.
Conclusion
API REST refers to RESTful APIs that follow constraints and principles of Representational State Transfer architectural style. This results in key benefits like separation of concerns, scalability and portability leveraging HTTP as the foundation. Despite some challenges, REST has become the predominant approach for web APIs due to these advantages. Continued evolution of standards, frameworks and best practices will enable REST APIs to power ever more complex web and mobile applications into the future.