1. Use nouns but no verbs
For an easy understanding use this structure for every resource:
| Resource | GET read |
POST create |
PUT update |
DELETE |
| /cars | Returns a list of cars | Create a new car | Bulk update of cars | Delete all cars |
| /cars/711 | Returns a specific car | Method not allowed (405) | Updates a specific car | Deletes a specific car |
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.
3. Use plural nouns
Keep it simple and use only plural nouns for all resources.
/users instead of /user
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
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. 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 a mount of 10.
200 – OK – Eyerything 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 enitity, 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.
7. Provide filtering, sorting, field selection and paging for collections
Filtering:
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
Sorting:
Allow ascending and descending sorting over multiple fields.
GET /cars?sort=-manufactorer,+model
This returns a list of cars sorted by descending manufacturers and ascending models.
Field selection
Mobile clients display just a few attributes in a list. They don’t need all 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.
GET /cars?fields=manufacturer,model,id,color
Paging
Use limit and offset. It is flexible for the user and common in leading databases. The default should be limit=20 and offset=0
GET /cars?offset=10&limit=5
To send the total entries back to the user use the custom HTTP header: X-Total-Count.