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Sebastien Dubois edited this page Jul 11, 2018 · 12 revisions




REST API Design Goals

REST Constraints

REST Resources

REST Resources Design Workflow

REST Resources Naming

REST Resources URIs

REST Resources Parameters

REST Resources Single items and collections

REST Resources Relations

REST Resources Many to many Relations

REST Resources Relations expansion

REST Resources Actions

REST API Versioning

REST API Documentation


HTTP Methods

HTTP Status Codes

HTTP Status Codes Success (2xx)

HTTP Status Codes Redirection (3xx)

HTTP Status Codes Client Error (4xx)

HTTP Status Codes Server Error (5xx)

Media types

CRUD Operations

CRUD About

CRUD Create Single item

CRUD Retrieve Single item

CRUD Retrieve Collection

CRUD Update Single item

CRUD Delete Single item


Pagination About

Pagination Rules and metadata

Pagination Example

Pagination Out of range/bounds


Filtering About

Filtering Using styles

Filtering Using includes

Filtering Using excludes


Sorting About

Sorting Metadata

Sorting Example


Searching About

Searching Local search

Searching Scoped search

Searching Global search

Searching Advanced search

Searching Wildcards

Searching Formatting

Long-running operations

Long-running Operations About

Long-running Operations Flow

Long-running Operations Rules

Long-running Operations Example

Concurrency control

Concurrency About

Concurrency Headers to use

Concurrency vs Delete operation

Concurrency vs Pagination

Caching and conditional requests

Caching and conditional requests About

Caching and conditional requests Rules

Caching and conditional requests HTTP headers

Conditional requests

Cache control

Error handling

Error handling About

Error handling Expectations

Error handling Status codes

Error handling Error details

Error handling Example with a single error

Error handling Example with multiple errors

Error handling Example with parameters

Error handling Example with additional metadata

Error handling Warnings


Compression About

Bulk operations

Bulk operations About

Bulk operations Types

Bulk operations Atomic

Bulk operations Non-atomic

Bulk operations Asynchronous

Bulk operations HTTP status codes

Bulk operations Resources naming convention

Bulk operations Errors

Bulk operations Creation example

Bulk operations Update example

Bulk operations Create and update example

File upload

File upload About

File upload File sizes

File upload Simple file upload

File upload Simple file upload example

File upload Complex file upload

File upload Complex file upload example

Security recommendations

REST Security General recommendations

REST Security Transport layer

REST Security Error handling

REST Security Insecure direct object references

REST Security CORS

REST Security Updates and consistency

REST Security API keys


Data formats


Rate limiting

Null values

Dates and times



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This is the REST API Design Guide of the National Bank of Belgium. This guide describes all design choices made for the creation of REST-like APIs at the National Bank of Belgium.


Choices choices choices...

There are many ways to implement RESTful APIs and, at this point in time, no clearly winning industry standard. There are many design choices to make:

  • high level design: pagination? filtering? search? sorting? ...
  • detailed design: page=2? offset=10? version in the URL or in a header? ...

When there are many options to choose from, development teams can argue forever about the best solution for each use case.

There are various standardization efforts that cover a lot of ground and multiple ways to formalize "REST" APIs (e.g., json-api, OData, OpenAPI, ...) but none that catered for all aspects we wanted to cover in the APIs of the National Bank of Belgium.

While preparing for the development of our APIs, we've decided to create our own design guide, with our own choices, covering our current and known future needs.

REST-like or truly RESTful?

Leonard Richardson has listed different "maturity levels" for REST APIs. This is covered in details here:

The Level 3, "Hypermedia Controls" introduces the notion of "discoverability" of the REST API, allowing your clients to "discover" the possible interactions within the responses provided by the server. This is often referred to as "HATEOAS" (Hypermedia As The Engine of Application State).

Roy Fielding (creator of REST) stated clearly that level 3 of the maturity model is actually mandatory for an API to be called a REST API:

Nevertheless, so far, we have chosen not to implement HATEOAS in our design; although this doesn't mean that we cannot add support for it at a later time. Take this choice with a grain of salt, it remains arbitrary. You might prefer implementing HATEOAS or similar solutions to go further with decoupling your client and server implementations and make your API truly RESTful.

There are tools and libraries that can help you with implementing support for level 3 in an easy way (e.g., Spring HATEOAS, ...).

So to be clear, this is not a truly RESTful API design guide.

If you're curious, we had a very interesting discussion over this here:


Our REST API Design Guide covers...

  • naming conventions and best practices (e.g., resource naming rules)
  • the design of all major elements you would need for business applications
    • CRUD
    • pagination & associated metadata
    • sorting
    • filtering
    • bulk operations
    • concurrency control
    • error handling
    • ...


Rules and guidelines in this design guide have different levels. Some are optional while some others are mandatory. Also, there are recommendations against some approaches, as well as things that are simply forbidden.

Here's how each term should be understood:

  • MUST: it's mandatory (i.e., hard rule)
  • MUST NOT: it's forbidden (i.e., hard rule)
  • SHOULD: it's heavily recommended (i.e., soft rule)
  • SHOULD NOT: there may exist valid reasons not to respect this but the implications should be well understood
  • MAY/OPTIONAL: it's optional (i.e., advice)

Take a look at RFC 2119 for more details.


Contributions are welcome. New designs or change proposals should be discussed via issues on this repository.