Most modern software systems rely on APIs to exchange data. Whether it is a mobile app loading a user profile, a web dashboard showing sales numbers, or a third-party service syncing orders, RESTful APIs are often the layer that connects everything together.
What does RESTful API mean?
API
An API (Application Programming Interface) defines how one system can request data or trigger actions in another system. It sets clear rules for requests and responses so both sides know what to expect.
REST / RESTful
REST stands for Representational State Transfer. A RESTful API follows a set of conventions that use standard HTTP methods and resource-based URLs, making the API predictable and easy to work with.
Endpoint
An endpoint is a specific URL that represents a resource or action, such as
/api/customers or /api/orders/125.
Payload
The payload is the data sent in the body of a request or response. Most REST APIs use JSON as the payload format.
HTTP methods
Common methods include GET (read data), POST (create), PUT or PATCH (update), and DELETE (remove).
Status codes
Numeric codes indicate the result of a request, such as 200 for success, 201 for created, 400 for bad request, or 401 for unauthorized.
Example with numbers:
{
"order_id": 345,
"items": 3,
"total": 129.75,
"currency": "USD"
}This response shows an order with 3 items and a total value of 129.75 USD. The payload size for a response like this is usually under 1 KB.
Where RESTful APIs are most applicable
RESTful APIs are well suited for systems where multiple clients need access to the same data or actions. They work well over HTTP and scale easily as usage grows.
- Web applications and admin dashboards
- Mobile applications on iOS and Android
- Third-party integrations such as payments, shipping, and analytics
- Internal services that need a clear separation of responsibilities
Should mobile apps and custom web development use the same APIs?
In most cases, using the same RESTful APIs for both mobile apps and custom web development is a good idea. A shared API layer keeps validation rules, permissions, and calculations consistent across all platforms.
That said, different clients often have different needs. Mobile apps may require smaller payloads to reduce data usage, while web applications may request more detailed data.
For example, a full order record might be 4 KB in size, while a mobile-friendly summary response can be reduced to about 1 KB by returning only the fields needed for a list view.
Tracking RESTful API performance
Performance is usually measured by response time and payload size. Both have a direct impact on user experience.
| Metric | Good range | Notes |
|---|---|---|
| Response time | 0.2 to 0.8 seconds | Simple read requests should stay under half a second when possible |
| Payload size | 1 to 50 KB | List endpoints should be kept small, especially for mobile clients |
| Error rate | Below 1% | Spikes often indicate database or validation issues |
Logging execution time, payload size, and HTTP status codes makes it easier to spot slow endpoints before users notice problems.
Securing RESTful APIs
Security should be considered from the start. APIs are often exposed to the internet and need clear protection.
- Use HTTPS for all requests to prevent data interception
- Require authentication using tokens such as API keys or JWT
- Validate and sanitize all incoming payloads
- Apply rate limiting to reduce abuse and brute-force attempts
- Never expose internal IDs or sensitive fields unless required
Even a simple rate limit, such as 100 requests per minute per client, can prevent many common attack patterns.
FAQ
No. REST is an architectural style. JSON is just a common data format used in REST APIs.
Yes. With proper pagination, caching, and monitoring, REST APIs can support very large and busy systems.
No. Many REST APIs are internal and only accessible within a private network or to trusted clients.
Versioning is strongly recommended. It allows you to introduce changes without breaking existing clients.