REST API URI Naming Conventions and Best Practices

1. What is a Resource?

In REST, the primary data representation is called resource. Having a consistent and robust REST resource naming strategy – will prove one of the best design decisions in the long term.

The key abstraction of information in REST is a resource. Any information that can be named can be a resource: a document or image, a temporal service (e.g. “today’s weather in Los Angeles”), a collection of other resources, a non-virtual object (e.g., a person), and so on.

In other words, any concept that might be the target of an author’s hypertext reference must fit within the definition of a resource.

A resource is a conceptual mapping to a set of entities, not the entity that corresponds to the mapping at any particular point in time.
— Roy Fielding’s dissertation

1.1. Singleton and Collection Resources

A resource can be a singleton or a collection.

For example, “customers” is a collection resource and “customer” is a singleton resource (in a banking domain).

We can identify “customers” collection resource using the URI “/customers“. We can identify a single “customer” resource using the URI “/customers/{customerId}“.

/customers			//is a collection resource

/customers/{id}		// is a singleton resource

1.2. Collection and Sub-collection Resources

A resource may contain sub-collection resources also.

For example, sub-collection resource “accounts” of a particular “customer” can be identified using the URN “/customers/{customerId}/accounts” (in a banking domain).

Similarly, a singleton resource “account” inside the sub-collection resource “accounts” can be identified as follows: “/customers/{customerId}/accounts/{accountId}“.

/customers						//is a collection resource

/customers/{id}/accounts		// is a sub-collection resource

1.3. URI

REST APIs use Uniform Resource Identifiers (URIs) to address resources. REST API designers should create URIs that convey a REST API’s resource model to the potential clients of the API. When resources are named well, an API is intuitive and easy to use. If done poorly, that same API can be challenging to use and understand.

The constraint of a uniform interface is partially addressed by the combination of URIs and HTTP verbs and using them in line with the standards and conventions.

Below are a few tips to get you going when creating the resource URIs for your new API.

2. Best Practices

2.1. Use nouns to represent resources

RESTful URI should refer to a resource that is a thing (noun) instead of referring to an action (verb) because nouns have properties that verbs do not have – similarly, resources have attributes. Some examples of a resource are:

Users of the system
User Accounts
Network Devices etc.

and their resource URIs can be designed as below:

/device-management/managed-devices 

/device-management/managed-devices/{device-id} 

/user-management/users

/user-management/users/{id}

For more clarity, let’s divide the resource archetypes into three categories (document, collection, and store). Then it would be best if you always targeted to put a resource into one archetype and then use its naming convention consistently.

For uniformity’s sake, resist the temptation to design resources that are hybrids of more than one archetype.

2.1.1. document

A document resource is a singular concept that is akin to an object instance or database record.

In REST, you can view it as a single resource inside a resource collection. A document’s state representation typically includes both fields with values and links to other related resources.

Use the “singular” name to denote the document resource archetype.

http://api.example.com/device-management/managed-devices/{device-id}
http://api.example.com/user-management/users/{id}
http://api.example.com/user-management/users/admin

2.1.2. collection

A collection resource is a server-managed directory of resources.

Clients may propose new resources to be added to a collection. However, it is up to the collection resource to choose whether to create a new resource or not.

A collection resource chooses what it wants to contain and also decides the URIs of each contained resource.

Use the “plural” name to denote the collection resource archetype.

/device-management/managed-devices
/user-management/users
/user-management/users/{id}/accounts

2.1.3. store

A store is a client-managed resource repository. A store resource lets an API client put resources in, get them back out, and decide when to delete them.

A store never generates new URIs. Instead, each stored resource has a URI. The URI was chosen by a client when the resource was initially put into the store.

Use “plural” name to denote store resource archetype.

/song-management/users/{id}/playlists

2.2. Consistency is the key

Use consistent resource naming conventions and URI formatting for minimum ambiguity and maximum readability and maintainability. You may implement the below design hints to achieve consistency:

2.2.1. Use forward slash (/) to indicate hierarchical relationships

The forward-slash (/) character is used in the path portion of the URI to indicate a hierarchical relationship between resources. e.g.

/device-management
/device-management/managed-devices
/device-management/managed-devices/{id}
/device-management/managed-devices/{id}/scripts
/device-management/managed-devices/{id}/scripts/{id}

2.2.2. Do not use trailing forward slash (/) in URIs

As the last character within a URI’s path, a forward slash (/) adds no semantic value and may confuse. It’s better to drop it from the URI.

http://api.example.com/device-management/managed-devices/ 
http://api.example.com/device-management/managed-devices         /*This is much better version*/

2.2.3. Use hyphens (-) to improve the readability of URIs

To make your URIs easy for people to scan and interpret, use the hyphen (-) character to improve the readability of names in long-path segments.

http://api.example.com/devicemanagement/manageddevices/
http://api.example.com/device-management/managed-devices 	/*This is much better version*/

2.2.4. Do not use underscores ( _ )

It’s possible to use an underscore in place of a hyphen to be used as a separator – But depending on the application’s font, it is possible that the underscore (_) character can either get partially obscured or completely hidden in some browsers or screens.

To avoid this confusion, use hyphens (-) instead of underscores ( _ ).

http://api.example.com/inventory-management/managed-entities/{id}/install-script-location  //More readable

http://api.example.com/inventory-management/managedEntities/{id}/installScriptLocation  //Less readable

2.2.5. Use lowercase letters in URIs

When convenient, lowercase letters should be consistently preferred in URI paths.

http://api.example.org/my-folder/my-doc       //1
HTTP://API.EXAMPLE.ORG/my-folder/my-doc     //2
http://api.example.org/My-Folder/my-doc       //3

In the above examples, 1 and 2 are the same, but 3 is not as it uses My-Folder in capital letters.

2.3. Do not use file extensions

File extensions look bad and do not add any advantage. Removing them decreases the length of URIs as well. No reason to keep them.

Apart from the above reason, if you want to highlight the media type of API using file extension, then you should rely on the media type, as communicated through the Content-Type header, to determine how to process the body’s content.

/device-management/managed-devices.xml  /*Do not use it*/

/device-management/managed-devices 	/*This is correct URI*/

2.4. Never use CRUD function names in URIs

We should not use URIs to indicate a CRUD function. URIs should only be used to identify the resources and not any action upon them uniquely.

We should use HTTP request methods to indicate which CRUD function is performed.

HTTP GET /device-management/managed-devices  			//Get all devices
HTTP POST /device-management/managed-devices  			//Create new Device

HTTP GET /device-management/managed-devices/{id}  		//Get device for given Id
HTTP PUT /device-management/managed-devices/{id}  		//Update device for given Id
HTTP DELETE /device-management/managed-devices/{id}  	//Delete device for given Id

2.5. Use query component to filter URI collection

Often, you will encounter requirements where you will need a collection of resources sorted, filtered, or limited based on some specific resource attribute.

For this requirement, do not create new APIs – instead, enable sorting, filtering, and pagination capabilities in resource collection API and pass the input parameters as query parameters. e.g.

/device-management/managed-devices
/device-management/managed-devices?region=USA
/device-management/managed-devices?region=USA&brand=XYZ
/device-management/managed-devices?region=USA&brand=XYZ&sort=installation-date

3. Do not Use Verbs in the URI

It is not correct to put the verbs in REST URIs. REST uses nouns to represent resources, and HTTP methods (GET, POST, PUT, DELETE, etc.) are then used to perform actions on those resources, effectively acting as verbs.

If we use verbs in the URI, we are most probably creating an RPC-style method call having a JSON or XML request/response format. It would be incorrect to call it REST.

/device-management/managed-devices/{id}/scripts/{id}/execute    //It is RPC, and not REST

In cases, where we need to perform some action that does not apply naturally to the definition of resources, we can create the custom URIs that can be considered nouns/resources and perform an action over them.

For example, instead of invoking /scripts/{id}/execute , we can create a resource for all scripts currently executing and submit a script to it if we want to execute a script.

/device-management/managed-devices/{id}/scripts/{id}/execute	//DON't DO THIS!

/device-management/managed-devices/{id}/scripts/{id}/status		//POST request with action=execute

You may also consider using the custom methods with colon(:) as described in custom methods by Google Cloud Docs, although many may find it in violation of REST principles.

4. Conclusion

In conclusion, we can say that resources are primarily nouns (objects) and we should avoid deviating from this principle. Anytime, we feel put verbs in the URI, we are creating an RPC call.