It’s 2025, just a few days away from 2026. Beyond the age of StackOverflow and deep into the age of AI, the industry has decades of experience, solid documentation, and well-known standards… yet REST APIs often look like they were designed in a hurry, on a late Friday afternoon, by someone with cold coffee making bad decisions.
This article isn’t about theory. We’ll review the 10 most common mistakes people still make and give you advice on how to avoid them without losing your mind (or your frontend team).
Let’s get into it.
1. Using POST for absolutely everything
This one just refuses to die, no matter how many times we think it’s been buried.
I still see APIs where every request is a POST call: fetching data, deleting resources, and updating states... all POST requests, all the time. Endpoints like POST /getOrders or POST /deleteOrders keep popping up as if HTTP methods were just a suggestion.
The definition of REST isn't “send JSON and hope for the best.”
HTTP methods exist for a reason, and they carry meaning:
- GET is for reading data,
- POST is for creating resources,
- PUT is for replacing them,
- PATCH is for partial updates,
- DELETE is for removals.
When every request is a POST, your API stops communicating intent and creates confusion. Clients can’t reason about the API’s behavior. At that point, your API isn’t really REST anymore; it’s just a dark tunnel full of JSON and regret.
2. Action-based endpoints instead of resource-based ones
Another classic example of bad practice is naming endpoints like this: /createOrder /updateOrder
But REST is about resources, not verbs: POST /orders PUT /orders/{id}
REST has been telling us for years that URLs should represent resources, not actions.
In REST, the resource goes in the path and the action is expressed by the HTTP method. You don’t need to encode behavior into the URL path because it’s already there. POST /orders is enough, and PATCH /orders/{id} says everything it needs to say.
If your endpoints start looking like function names or method calls, that’s usually a sign that the API is leaking implementation details instead of exposing a clean contract. URLs should describe what you’re interacting with, not how your backend happens to do it.
3. APIs that always return 200
Honestly? This should be illegal.
200 OK
{ "error": true }
An endpoint that responds 200 OK no matter the context (including obvious failures) forces the client to guess whether things actually worked. Seeing a 200 response with something like
{ “error”: true }
inside the body defeats the entire purpose of HTTP status codes.
Status codes are not for decoration. They exist for a reason: to communicate the outcome clearly and consistently. Creation, validation errors, authorization problems, and missing resources - all of these already have a well-defined status in HTTP.
When everything is a 200, the frontend has to inspect payloads, add conditionals everywhere, and reverse-engineer intent. Guessing in production is exactly how hard-to-reproduce bugs are born.
4. Errors with no message (or useless ones)
Few things are more frustrating than getting an error response that tells you absolutely nothing.
A generic { “message” : “Error” } might technically be a response, but it’s not useful. It doesn’t explain what failed, why it failed, or what the client is supposed to do next. It’s just noise.
A decent error response should provide context, a human-readable message, and enough information to act on it. Clear error messages aren’t about being verbose; they’re about saving time, avoiding misinterpretation, and making systems easier to maintain.
A better example would be:
{
"code": "USER_NOT_FOUND",
"message": "The provided user ID was not found."
}
Clear errors aren’t a luxury; they are technical empathy.
5. Not versioning the API
Versioning your API is mandatory. Breaking compatibility is not.
A lot of teams avoid versioning entirely until the day they introduce a breaking change and suddenly everything catches fire. Others go to the opposite extreme and bump versions for every tiny tweak, creating a mess of duplicated logic and abandoned clients.
Most changes don’t require a new version if the API is designed properly. You can add new fields, keep them optional, and extend behavior without breaking existing consumers. But when you do introduce real breaking changes (removing fields, changing data types, or altering core flows), that’s when versioning becomes mandatory.
When you introduce a breaking change, version it explicitly: /api/v1/users /api/v2/users
Design for backward compatibility first. Version only when you truly need to break things. Anything else is either naive optimism or technical debt in disguise.
6. Returning inconsistent response structures
This one is especially cruel to whoever consumes the API. One endpoint returns:
{ "data": [...] }
Another:
{ "users": [...] }
and another:
[ ... ]
One endpoint wraps responses under data, another under user, and another returns a raw array. Individually, each response might make sense. Collectively, they create chaos.
The frontend ends up full of conditionals, optional chaining, defensive checks, and workarounds that have nothing to do with business logic - all because the API couldn’t make up its mind.
Defining a response contract and sticking to it is not overengineering. Consistency is UX for developers, and inconsistent APIs are exhausting to work with.
7. No pagination
If your API returns thousands of records “because there aren’t many yet”… we’ll talk again in six months. It is a classic "future-you" problem.
It works fine until it doesn’t. Data grows, performance degrades, payloads get heavier, and suddenly a simple request becomes slow, expensive, and painful to handle.
List endpoints should always be designed with pagination, filtering, and sorting in mind, even if the dataset is small today. APIs exist to do the heavy lifting and expose controlled access to data, not to dump massive responses on the frontend and hope for the best.
A good example:
GET /users?page=1&limit=20&sort=createdAt
8. Business logic stuffed into controllers
Endless controllers, no real service layer, and business rules mixed directly with HTTP concerns. A timeless classic.
Controllers should be thin. Their job is to receive the request, validate input, delegate work to services, and return a response. When controllers start handling business decisions, data transformations, and complex workflows, they become hard to read, hard to test, and hard to maintain.
If your controller reads like a novel, something is wrong.
9. Blindly trusting the frontend
“It’s fine, the frontend already validates this.” Famous last words.
The frontend is not a security boundary. Anything running on the client can be bypassed, modified, or abused. The backend must always validate inputs, sanitize data, and enforce rules consistently.
The API is the last line of defense, and production is full of very creative users. Trusting the frontend blindly is not optimism; it’s negligence.
10. APIs without documentation
If it’s not documented, it doesn’t exist.
An undocumented API forces consumers to read code, guess behavior, or ask questions that shouldn’t be necessary. Swagger is not optional; it is part of the API itself.
Clear descriptions, real examples, and up-to-date contracts make the difference between an API people enjoy using and one they tolerate. An API without documentation is like IKEA furniture without instructions: someone will assemble it wrong, guaranteed.
In 2026, “this is how we’ve always done it” won’t cut it anymore
Today, an API shouldn’t surprise anyone - not the frontend, not the QA and not the person maintaining it (spoiler: that’s you).
A good API should be predictable, consistent, rely on standards instead of clever hacks, and never force you to read the entire codebase just to understand what’s going on. This isn’t about being a senior developer; it’s about meeting a basic professional standard.
Looking ahead to 2026 (honestly, this should already have been the goal in 2025), the expectation is clear: APIs with well-defined contracts, human-readable error messages, thoughtful versioning, and absolute consistency. In short, APIs that can evolve without breaking everything along the way.
A poorly designed API is no longer just annoying; it becomes a bottleneck, a cost, and a constant source of bugs - both ridiculous and subtle. Designing an API for 2026 isn’t about being clever; it’s about being responsible.
Because good APIs don’t cause surprises. They just work.
