Here’s the deal with APIs: a lot of people are making them, but most of them are doing it wrong.
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You may have been there. You’re trying to connect to an API, but all of a sudden you’re overwhelmed by endpoints that don’t work, error messages that don’t make sense, and documentation that looks like it was written in ancient hieroglyphics. Isn’t that annoying?
The truth is that good API design isn’t just about making your endpoints work; it’s also about making an experience that developers want to use. And that starts with knowing the basic rules that set apart amateur APIs from the ones that run billion-dollar platforms.
This guide will explain all the important things you need to know about designing APIs. You’ll learn real-world strategies that you can use whether you’re building your first REST API or fixing up an old one.
What Are API Design Principles and Why Should You Care?
API design principles are the basic rules and best practices that tell you how to set up, document, and keep your application programming interfaces in good shape. Think of them as the plan for making APIs that are easy to use, grow, and—most importantly—easy for other developers to understand.
This is important because a well-designed API can speed up development cycles, cut down on support tickets by 60–70%, and make it much easier for developers to use. What about the other side? A poorly designed API is technical debt that will follow your team for years.
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The Main Parts of Good API Design
But here’s something most tutorials won’t tell you: these rules don’t work for everyone. There are different things to think about when using a GraphQL API than when using a REST API. For example, a public API needs stricter versioning than an internal microservice. It matters what the situation is.
REST API Design: The Base That Most Developers Use
REST (Representational State Transfer) is still the most popular way to build APIs for web services. Why? Because it’s easy to understand and works with how the web already works when done right.
Resource-Oriented Design: Use Nouns Instead of Verbs
This is where new people always mess up. Your API endpoints should show things (resources), not actions.
❌ Wrong Way:
textPOST /createUser
GET /getUserById/123
POST /updateUserEmail
✅ Right Way:
textPOST /users
GET /users/123
PATCH /users/123
Do you see the difference? The HTTP methods (GET, POST, PUT, PATCH, DELETE) already tell us what to do. Your URLs should only point to the resource. This makes a pattern that is always the same and easy for developers to remember.
HTTP Methods: Use Them Right
There is a reason for each HTTP method. It’s not enough to just follow the rules when using them; you also have to make APIs that work the same way every time.
| HTTP Method | Purpose | Idempotent |
|---|---|---|
| GET | Retrieve data (never change anything) | Yes |
| POST | Create new resources | No |
| PUT | Replace the entire resource | Yes |
| PATCH | Update specific fields | No |
| DELETE | Remove a resource | Yes |
Pro Tip: GET requests should always be idempotent, which means that calling them more than once will always give you the same result. You can safely try again on failed requests without worrying about what might happen.
Naming Conventions That Make Sense
The names you choose for your API will make or break its readability. Here’s what works:
Use plural nouns when talking about collections:
/usersnot/user/productsinstead of/product
Use lowercase letters and hyphens (kebab-case) for URIs:
/order-itemsnot/OrderItemsor/order_items
Be consistent with nesting:
| Example | Status |
|---|---|
/users/123/orders | ✅ Good |
/users/123/orders/456 | ✅ Good |
/123/orders/456/items/789 | ❌ Too deep (use query params instead) |
If you need more than three levels of nesting, you’re probably not modelling your resources correctly. Make it flat.
API-First Development: Why Code Should Come After Design
At first, the code-first approach seems faster. You just need to start making endpoints, right? No.
When you do API-first development, you write the implementation code after you define your API contract, which is the specification of what your API does. This may seem like extra work, but it will save you a lot of trouble later.
The API-First Method
This method has a huge benefit: the frontend and backend teams can work on the same project at the same time. Your backend engineers can write the real code while your frontend developers work with mock servers.
Quick Tip: Using tools like Postman, Swagger Editor, and Stoplight makes designing APIs much easier. Don’t use a plain text editor to write OpenAPI specs; you’ll hate your life.
Security Principles You Can’t Ignore
I’ve seen too many APIs that don’t think about security until after they ship. That’s how hackers get into data.
Authentication vs. Authorisation
| Concept | Question It Answers |
|---|---|
| Authentication | “Who are you?” |
| Authorisation | “What are you allowed to do?” |
You need both of them. OAuth 2.0 with JWT tokens is the most common pattern in 2025, but let’s be honest—getting OAuth to work right is hard.
| Use Case | Recommended Approach |
|---|---|
| Simple internal APIs | API keys with rate limiting |
| Public APIs | OAuth 2.0 (industry standard) |
| Microservices | Mutual TLS (mTLS) |
Always Use HTTPS
For real. SSL/TLS should encrypt every API request. It’s 2025, and there’s no reason to send data in plain text. You should use HTTPS for all APIs, even internal ones, because internal networks aren’t as safe as you think.
Rate Limiting is Not Optional
Rate limiting keeps your infrastructure safe from both intentional attacks and unintentional abuse, like a buggy client that gets stuck in a loop.
Common approaches:
- Per API key: 1000 requests per hour
- Per endpoint: Stricter limits on costly operations
- Burst allowance: Allow short spikes but limit long periods of high use
Return rate limit information in response headers:
textX-RateLimit-Limit: 1000
X-RateLimit-Remaining: 247
X-RateLimit-Reset: 1643723400
Error Handling: The Art of Failing Gracefully
One of the quickest ways to annoy developers who use your API is to not handle errors properly.
HTTP Status Codes: Use Them Correctly
Don’t just say “200 OK” for everything and then put the real status in the response body. That’s a mistake that new people make.
| Status Code | Meaning | When to Use |
|---|---|---|
| 200 OK | Success | GET, PATCH, or DELETE worked |
| 201 Created | Resource created | Successful POST that made a resource |
| 204 No Content | Success, no body | DELETE worked, no response body |
| 400 Bad Request | Client error | Client sent bad data |
| 401 Unauthorised | Auth required | Need to log in or login failed |
| 403 Forbidden | Access denied | Logged in but not allowed |
| 404 Not Found | Missing resource | Resource doesn’t exist |
| 429 Too Many Requests | Rate limited | Rate limit has been reached |
| 500 Internal Server Error | Server error | Something went wrong on your end |
Error Response Structure
Your error responses should be consistent and useful every time. Here’s a good pattern:
json{
"error": {
"code": "INVALID_EMAIL_FORMAT",
"message": "The email address you gave is not valid",
"details": {
"field": "email",
"value": "not-an-email",
"hint": "Email must have a valid domain and a @ symbol"
},
"request_id": "req_1a2b3c4d5e"
}
}
What this includes:
- Error code (machine-readable): For programmatic handling
- Message (human-readable): For debugging
- Specific details: What went wrong and where it happened
- Request ID: For help and keeping track of things
API Versioning: Make Changes Without Breaking Things
Your API will change over time. You need to make breaking changes sometimes, and new features are added while old ones are removed. How you handle versioning can make your users love you or hate you.
Versioning Strategies Comparison
| Strategy | Example | Pros | Cons |
|---|---|---|---|
| URI Versioning | /v1/users, /v2/users | Clear, easy to follow | Makes URIs messy |
| Header Versioning | Accept: application/vnd.myapi.v2+json | Cleaner URIs | Harder to see and test in browsers |
| Query Parameter | /users?version=2 | Easy to implement | Mixes versioning with resource querying |
Recommendation: URI versioning for public APIs (for clarity) and header versioning for internal APIs (for cleanliness).
The Golden Rule of Versioning
Never remove or change existing endpoints without giving them time to get used to the change. Before making changes that will break things, give developers at least 6 to 12 months’ notice. Send deprecation headers:
textDeprecation: Sun, June 1, 2025, 23:59:59 GMT
Link: <https://api.example.com/v2/users>; rel="successor-version"
Documentation: The User Guide for Your API
You could make the most beautiful API in the world, but no one will use it if the documentation is bad.
What Makes Good API Documentation
| Component | Description |
|---|---|
| Getting Started Guide | Sign in and make first call in less than 5 minutes |
| Endpoint Reference | All parameters and all responses documented |
| Code Examples | At least 3 languages (JavaScript, Python, cURL) |
| Use Case Tutorials | Real-world examples |
| Error Catalogue | List of all possible error codes and meanings |
| Changelog | List of changes made in each version |
Pro Insight: Interactive documentation like Swagger UI lets developers make real API calls. This cuts down on the time it takes to make the first successful call significantly.
Developer Experience Matters
Think about it: developers are the ones who use your API. Adoption depends on their experience.
- Make everyday tasks easier: This is where the 80/20 rule comes in
- Provide SDKs: Don’t make people write HTTP requests by hand
- Include working examples: Copy and paste should work
- Give people a sandbox: Let them try things out without any consequences
GraphQL vs. REST: Choosing the Right Approach
There are other things to do besides REST. GraphQL has become very popular, especially for applications with a lot of front-end work.
When to Choose GraphQL vs REST
| Choose GraphQL When | Choose REST When |
|---|---|
| Clients need flexible data queries (mobile apps with different needs) | You need basic CRUD tasks |
| Building a data-intensive application | Caching is very important (HTTP caching is well-known) |
| You want to reduce over-fetching and under-fetching | Your team knows more about REST |
| You have diverse clients (web, mobile, desktop) | You’re building simple microservices |
There isn’t a “better” choice for everyone. Choose based on what you need, not what everyone else is saying.
Performance and Scalability Principles
Your API might work perfectly with ten users. What about 10,000? Or 10 million ?
Pagination: Don’t Send Back Everything
Getting 50,000 records back in one request is a sure way to fail. Use pagination from the start.
Offset-based (simple but has problems at scale):
text/users?limit=20&offset=100
Cursor-based (better for big datasets):
text/users?cursor=eyJpZCI6MTIzfQ&limit=20
Return pagination metadata in responses:
json{
"data": [...],
"pagination": {
"next_cursor": "eyJpZCI6MTQzfQ",
"has_more": true
}
}
Caching Strategy
Use HTTP caching headers correctly:
| Header | Purpose |
|---|---|
| Cache-Control | How long responses can be stored |
| ETag | For conditional requests (304 Not Modified) |
| Last-Modified | Alternative to ETag |
Quick Tip: Data that doesn’t change often (like lists of countries) should be cached aggressively. User-specific data needs shorter cache times or none at all.
Compression Saves Bandwidth
Turn on gzip or brotli compression. A 500KB JSON response can be compressed down to 50KB—that’s 90% less bandwidth and faster loading times.
Common API Design Patterns
Filtering and Sorting
text/products?category=electronics&price_min=100&price_max=500&sort=-price
Use query parameters to narrow down your results. The minus sign convention (-price) for sorting in descending order is clear and easy to understand.
Partial Responses (Field Selection)
Let clients request only the fields they need:
text/users/123?fields=id,name,email
This reduces payload size and can greatly improve performance.
Batch Operations
When you need to operate on multiple resources at once, support batch operations:
json{
"operations": [
{"action": "create", "data": {...}},
{"action": "update", "id": 123, "data": {...}}
]
}
Asynchronous Operations
For tasks that take a long time to run, return “202 Accepted” with a status URL:
json{
"status_url": "/reports/123/status",
"estimated_completion": "2025-02-05T15:30:00Z"
}
Clients can check the status URL until the job is done.
Common Mistakes to Avoid
| Mistake | Why It’s Bad |
|---|---|
| Not paying attention to backward compatibility | Every breaking change costs you users |
| Nesting resources too deeply | Keep URLs short, use query parameters |
| Returning different data structures | Consistency is key |
| Generic error messages like “Error occurred” | Doesn’t help anyone debug |
| No rate limiting | Your servers will suffer later |
| Not doing API versioning | “We’ll add it later” never happens |
| Inconsistent naming | Hard to tell difference between getUserInfo, getUser, and fetchUserData |
Frequently Asked Questions
What is the difference between REST and RESTful APIs?
REST is a way of designing things, and RESTful means that your API actually follows REST principles. Many “REST APIs” aren’t really RESTful; they just use HTTP. Real RESTful APIs don’t keep track of state, use the right HTTP methods, and follow resource-oriented design.
Should I use PATCH or PUT to make changes?
Use PUT to replace a whole resource and PATCH to change specific fields. PATCH is better for partial updates because it uses less bandwidth and is more flexible.
How do I handle API versioning for mobile apps?
You can’t make people update their mobile apps right away, so maintain backward compatibility for longer. Consider using header versioning so you can upgrade API versions without code changes. Plan for at least 12 to 18 months of support for older versions.
What is the best way to authenticate APIs?
OAuth 2.0 with JWT tokens is the industry standard for public APIs. API keys are fine for simple use cases or internal APIs. Consider mutual TLS for microservices. The “best” method depends on your security requirements and complexity tolerance.
How detailed should API error messages be?
Detailed enough to help debugging, but not so detailed that you expose security information. For validation errors, include error codes, explanatory messages, and field details. Don’t show stack traces or database errors in production.
When is GraphQL better than REST?
Choose GraphQL if you need flexible data retrieval (like when mobile apps request different fields), if you’re working with complex nested data, or if you want to avoid multiple API calls. REST is easier for basic CRUD tasks and has better HTTP caching.
How can I deprecate API endpoints without breaking integrations?
Give at least 6 to 12 months’ notice, send deprecation headers in responses, maintain detailed changelogs, create migration guides, and provide support during the transition. Don’t remove endpoints without warning; it breaks trust.
Key Takeaways
| Principle | Action |
|---|---|
| API-First Development | Design the API contract before writing code |
| Consistency | Predictable patterns make your API easy to learn |
| Error Handling | Help developers debug quickly with clear error responses |
| Security | HTTPS, authentication, and rate limiting are non-negotiable |
| Documentation | Invest in clear, example-filled docs |
| Versioning | Plan carefully; breaking changes without warning ruin trust |
| Performance | Pagination, caching, and compression are required |
Making great APIs is both science and art. The science is based on proven patterns. The art is knowing when to break the rules to make the developer experience better.