Plural vs singular resource names in Rest API - When to Use Which

The Big Idea

Why does one tiny naming choice make your whole API easier or harder to use?

The Scenario

Imagine you are building a website where users can manage books. You decide to name your API endpoints randomly--sometimes using singular names like /book, other times plural like /books. This inconsistency confuses both you and anyone else using your API.

The Problem

Without a clear rule, your API becomes hard to remember and maintain. Clients might guess the wrong endpoint, causing errors. Documentation gets messy, and your team wastes time fixing misunderstandings instead of building features.

The Solution

Using a consistent rule--like always using plural names for resource collections (/books) and singular for single items (/books/123)--makes your API predictable and easy to use. Everyone knows what to expect, reducing mistakes and speeding up development.

Before vs After

✗ Before

GET /book
POST /books
GET /books/123
DELETE /book/123

✓ After

GET /books
POST /books
GET /books/123
DELETE /books/123

What It Enables

This consistency lets developers quickly understand and use your API, making collaboration smoother and your app more reliable.

Real Life Example

Think of a library app where /books returns all books, and /books/123 returns one specific book. This clear pattern helps both frontend and backend teams work together without confusion.

Key Takeaways

Inconsistent naming causes confusion and errors.

Using plural names for collections and singular for items creates clarity.

Consistent API design improves teamwork and speeds development.

Practice

1. Which naming style is recommended for an API endpoint that returns a list of users?
/user or /users?

easy

A. /users because it is singular and more precise.

B. /user because it is shorter and simpler.

C. /user because it is singular and more precise.

D. /users because it represents multiple users.

Solution

1. Step 1: Understand resource naming for collections

   API endpoints returning multiple items should use plural names to clearly indicate a list.

2. Step 2: Apply naming to the example

   Since the endpoint returns multiple users, /users is the correct plural form.

3. Final Answer:

   /users because it represents multiple users. -> Option D

4. Quick Check:

   Plural for lists = /users [OK]

Hint: Use plural names for endpoints returning lists [OK]

Common Mistakes:

• Using singular for list endpoints
• Confusing singular and plural forms
• Choosing shorter names over clarity

2. Which of the following is the correct endpoint to access a single product by its ID?

easy

A. /products/123

B. /product/123

C. /products

D. /product

Solution

1. Step 1: Identify singular vs plural for single item access

   When accessing a single item by ID, use the plural form of the resource name followed by the ID.

2. Step 2: Match the correct endpoint format

   The endpoint /products/123 uses plural products and includes the ID, which is the common RESTful convention.

3. Final Answer:

   /products/123 -> Option A

4. Quick Check:

   Single item access = plural + ID [OK]

Hint: Use plural resource name when accessing one item by ID [OK]

Common Mistakes:

• Using singular resource name for single item
• Omitting the ID when accessing a single item
• Mixing singular/plural inconsistently

3. Given the following API endpoints, which one correctly retrieves a list of orders?

GET /order
GET /orders
GET /order/456
GET /orders/456

medium

A. GET /order

B. GET /orders/456

C. GET /orders

D. GET /order/456

Solution

1. Step 1: Identify endpoints returning lists

   Endpoints returning lists should use plural resource names without an ID.

2. Step 2: Analyze each option

   GET /orders uses plural and no ID, so it returns the list of orders. Others either use singular or include an ID, indicating single item access.

3. Final Answer:

   GET /orders -> Option C

4. Quick Check:

   List retrieval = plural resource without ID [OK]

Hint: Plural + no ID means list retrieval [OK]

Common Mistakes:

• Choosing singular endpoint for list
• Confusing ID presence with list retrieval
• Ignoring plural vs singular rules

4. You have an API endpoint defined as GET /users/ to get a list of users and GET /user/{id} to get a single user. A developer mistakenly uses GET /user/ to get all users. What is the likely problem?

medium

A. The endpoint /user/ is incorrect for list retrieval and may cause a 404 error.

B. The endpoint /user/ will return a list of users anyway.

C. The endpoint /user/ will return a single user without ID.

D. The endpoint /user/ will automatically redirect to /users/.

Solution

1. Step 1: Understand endpoint naming conventions

   List retrieval requires plural resource name, so /users/ is correct for all users.

2. Step 2: Analyze the incorrect usage

   /user/ is singular and without an ID, so it likely does not exist or returns an error like 404.

3. Final Answer:

   The endpoint /user/ is incorrect for list retrieval and may cause a 404 error. -> Option A

4. Quick Check:

   Singular without ID ≠ list endpoint [OK]

Hint: Singular without ID usually causes errors for list requests [OK]

Common Mistakes:

• Using singular endpoint for list retrieval
• Assuming singular endpoint returns list
• Expecting automatic redirects between endpoints

5. You are designing an API for a library system. Which of the following endpoint designs correctly follows the plural vs singular resource naming best practices for retrieving a single book and all books?

hard

A. GET /book for all books and GET /books/{id} for a single book

B. GET /books for all books and GET /book/{id} for a single book

C. GET /books/{id} for all books and GET /book for a single book

D. GET /book/{id} for all books and GET /books for a single book

Solution

1. Step 1: Recall naming rules for collections and single items

   Use plural resource names for collections (all books) and singular for single items by ID.

2. Step 2: Match options to rules

   GET /books correctly retrieves all books (plural). GET /book/{id} correctly retrieves a single book (singular with ID).

3. Final Answer:

   GET /books for all books and GET /book/{id} for a single book -> Option B

4. Quick Check:

   Plural for list, singular + ID for single [OK]

Hint: Plural for lists, singular + ID for single items [OK]

Common Mistakes:

• Swapping singular and plural for list vs single
• Using singular without ID for list
• Using plural with ID for single item