Web APIs have become a very important topic in the last year. We are working every day with different backend systems and therefore we know about the importance of clean API design.
Typically we use a RESTful design for our web APIs. The concept of REST is to separate the API structure into logical resources. There are used the HTTP methods GET, DELETE, POST and PUT to operate with the resources.
These are 10 best practices to design a clean RESTful API:
1. Use nouns but no verbs
For an easy understanding use this structure for every resource:
||Returns a list of cars
||Create a new car
||Bulk update of cars
||Delete all cars
||Returns a specific car
||Method not allowed (405)
||Updates a specific car
||Deletes a specific car
Do not use verbs:
2. GET method and query parameters should not alter the state
Use PUT, POST and DELETE methods instead of the GET method to alter the state.
Do not use GET for state changes:
GET /users/711?activate or
3. Use plural nouns
Do not mix up singular and plural nouns. Keep it simple and use only plural nouns for all resources.
/cars instead of /car
/users instead of /user
/products instead of /product
/settings instead of /setting
4. Use sub-resources for relations
If a resource is related to another resource use subresources.
GET /cars/711/drivers/ Returns a list of drivers for car 711
GET /cars/711/drivers/4 Returns driver #4 for car 711
5. Use HTTP headers for serialization formats
Both client and server, need to know which format is used for the communication. The format has to be specified in the HTTP-Header.
Content-Type defines the request format.
Accept defines a list of acceptable response formats.
6. Use HATEOAS
tate is a principle that hypertext links should be used to create better navigation through the API.
7. Provide filtering, sorting, field selection and paging for collections
Use a unique query parameter for all fields or a query language for filtering.
GET /cars?color=red Returns a list of red cars
GET /cars?seats<=2 Returns a list of cars with a maximum of 2 seats
Allow ascending and descending sorting over multiple fields.
This returns a list of cars sorted by descending manufacturers and ascending models.
Mobile clients display just a few attributes in a list. They don’t need all the attributes of a resource. Give the API consumer the ability to choose returned fields. This will also reduce the network traffic and speed up the usage of the API.
Use limit and offset. It is flexible for the user and common in leading databases. The default should be limit=20 and offset=0
To send the total entries back to the user use the custom HTTP header: X-Total-Count.
Links to the next or previous page should be provided in the HTTP header link as well. It is important to follow this link header values instead of constructing your own URLs.
Link: ; rel="next",
8. Version your API
Make the API Version mandatory and do not release an unversioned API. Use a simple ordinal number and avoid dot notation such as 2.5.
We are using the url for the API versioning starting with the letter „v“
9. Handle Errors with HTTP status codes
It is hard to work with an API that ignores error handling. Pure returning of a HTTP 500 with a stacktrace is not very helpful.
Use HTTP status codes
The HTTP standard provides over 70 status codes to describe the return values. We don’t need them all, but there should be used at least an amount of 10.
200 – OK – Everything is working
201 – OK – New resource has been created
204 – OK – The resource was successfully deleted
304 – Not Modified – The client can use cached data
400 – Bad Request – The request was invalid or cannot be served. The exact error should be explained in the error payload. E.g. „The JSON is not valid“
401 – Unauthorized – The request requires an user authentication
403 – Forbidden – The server understood the request, but is refusing it or the access is not allowed.
404 – Not found – There is no resource behind the URI.
422 – Unprocessable Entity – Should be used if the server cannot process the entity, e.g. if an image cannot be formatted or mandatory fields are missing in the payload.
500 – Internal Server Error – API developers should avoid this error. If an error occurs in the global catch blog, the stracktrace should be logged and not returned as response.
Use error payloads
All exceptions should be mapped in an error payload. Here is an example of how a JSON payload should look like.
"Sorry, the requested resource does not exist"
"No car found in the database"
10. Allow overriding HTTP method
Some proxies support only POST and GET methods. To support a RESTful API with these limitations, the API needs a way to override the HTTP method.
Use the custom HTTP Header X-HTTP-Method-Override to override the POST Method.