API Considerations for Beginners

Fredrik Bergqvist 05 September 2025

When you’re starting out designing an API, there are a few things you’ll want to think about early on. Some of these will save you time down the road, others will help you avoid common mistakes that lead to bugs, confusion, or security holes. Here are the main points I keep in mind.

Versioning

Think about how you want to handle versioning from the start. Even if you don’t expect to support multiple versions right away, it’s often a good idea to include a version prefix in your paths, such as /v1/. That way, if you ever need to introduce breaking changes, you won’t have to redesign your whole URL structure.

Documentation

Take the time to document your API. Swagger (OpenAPI) is the most common way and comes with several benefits:

It’s easy to import into tools like Postman.
You can generate frontend methods, complete with TypeScript types and helpers.
- Kubb.dev has many plugins for automatic generation.
- I’ve also used swagger-typescript-api to generate types and TanStack Query hooks.
Swagger includes an SDK generator: swagger.io/tools/swagger-codegen.

On top of that, it’s worth keeping a simple README file with instructions on how to set up, build, and run your API server. It’s easy to forget these details, even for your own projects.

Caching

Caching can give you a big performance boost, but how you do it depends on the size and reliability of your system.

For small apps where it doesn’t matter if data has to be re-fetched on a restart, in-memory caching is usually enough. For bigger systems, or anything running multiple instances, you’ll want something more robust like Redis or Memcached so your caches stay in sync.

Use correct HTTP methods and responses

Using the right HTTP methods and returning the right status codes makes your API predictable and easier to use. Here’s the basic breakdown:

GET to fetch an entity → 200 OK
POST to create an entity → 201 Created with a Location header pointing to the new resource’s URL
PUT to replace an entity → 200 OK or 204 No Content
PATCH to update specific attributes on an entity → 200 OK or 204 No Content
DELETE to remove an entity → 200 OK or 204 No Content

You should also decide whether you want to return the full model after an update, or just 204 No Content. Either way is fine — the important thing is to be consistent.

Be careful with your error handling. Don’t return a generic 500 if the problem is really that the resource wasn’t found — that should be a 404. Similarly, use 409 Conflict when two updates clash, and return 400 Bad Request for validation errors.

Finally, pick a consistent error response format and stick with it. A simple structure like:

{
  "code": "invalid_input",
  "message": "Email is not valid",
  "details": {}
}

goes a long way toward making your API easier to consume.

Security

Always use HTTPS. This is the baseline for protecting data in transit.

If your API will be called from browsers, set up CORS to restrict which domains are allowed. Keep in mind that CORS is only a browser-level safeguard — other clients can still make requests — so you should always enforce security on the server too.

Authentication is another must. At the simplest level, you can require an API key. That’s easy to implement, but not very secure and only suitable for low-value data. For anything more important, go with JWTs or OAuth, which give you more control over permissions, expiry, and token management.

When it comes to error handling, don’t leak sensitive details. Stack traces and debug output don’t belong in responses. Always sanitize and validate inputs on the server, no matter how much you “trust” the client.

And finally, consider adding rate limiting or throttling. This prevents brute-force attacks and stops clients from overwhelming your service.

Monitoring and observability

If your API is critical, you’ll want visibility into how it’s behaving. Logging is the first step — make sure you record enough to debug issues later. But don’t stop there: set up alerts for spikes in errors or traffic, and keep an eye on key metrics like latency, error rates, and request volume. This will help you catch issues before users report them.

Listings

When your API returns lists of entities, you should almost always implement pagination. Dumping thousands of records in one response is wasteful and slow.

Sometimes, you don’t even need the full model. For example, if you’re filling a dropdown menu, you probably only need an id and a name. In these cases, consider adding lightweight listing endpoints that only return the fields needed. This makes responses faster and easier to work with.

Updating several items at once

Sometimes users want to perform bulk actions, like selecting multiple items and archiving them. There are a couple of ways to handle this.

For small updates, you can just use PATCH and only update the relevant property. The server should always apply the change against the latest version of the data.

For larger operations, a dedicated batch endpoint is often better. That way you can update multiple records in a single call, keeping everything consistent and reducing round trips.

Whichever approach you use, make sure the client has fresh data. A common pattern is to refetch whenever the browser tab regains focus, so users don’t accidentally update stale state.

Avoiding overwriting updates (concurrency)

A common issue in APIs is two people editing the same resource at the same time. Without safeguards, whoever saves last overwrites the other person’s changes.

One simple approach is to include a lastUpdated timestamp (or a version number) in each model. The client includes this value in its update request, and the server checks it against the database. If it doesn’t match, you know the resource has changed since the client last fetched it, and you can reject the update.

Another approach is to use ETags with the If-Match header. This is built into HTTP and works much the same way: the ETag identifies the version of the resource, and if it doesn’t match on update, the server returns 412 Precondition Failed.

For business-critical actions like payments, you should also consider supporting an Idempotency-Key header. This ensures retries don’t cause duplicate side effects if the client resends the same request after a timeout or network issue.

Testing

Even a little bit of testing can go a long way. Start with integration tests that just check status codes. This is enough to make sure all your endpoints respond correctly and helps you catch routing or method errors early.

For more important endpoints, add contract tests that validate not just the status but the shape and content of the response. That way, if someone changes a field name or removes a property, you catch it before clients break. If you have multiple services talking to each other, consumer-driven contract testing tools like Pact can be very helpful.

Automate tests where it makes sense. Even a small set of tests running in your CI pipeline can prevent regressions. Tools like Postman are great for exploration and manual checks, but don’t stop there — add unit tests and automated integration tests to round out your strategy.

Wrapping up

Designing APIs is partly about following conventions and partly about thinking ahead. By choosing consistent HTTP methods, handling concurrency, validating input, and writing at least some tests, you’ll avoid many of the pitfalls that trip up beginners.

You don’t need to over-engineer everything on day one, but if you keep these practices in mind, you’ll end up with an API that’s easier to maintain, safer to use, and friendlier to clients.