Understanding REST API HTTP Methods: GET, POST, PUT, DELETE, and more

TL;DR

1. REST APIs utilize standard HTTP methods (verbs) to define actions on resources, making interactions predictable and intuitive.

2. GET retrieves data, POST creates new resources, PUT updates or replaces existing resources, and DELETE removes them.

3. Idempotency (repeated requests yield same result) and safety (no server-side state change) are crucial concepts, defining how methods like GET, PUT, and DELETE behave reliably.

4. Beyond the core four, methods like PATCH (partial update), HEAD (header only), and OPTIONS (supported methods) offer more nuanced control.

5. Choosing the correct HTTP method and handling status codes are fundamental for designing robust, scalable, and understandable RESTful services.

At the heart of many modern applications lies the REST architectural style, a powerful approach for building web services that thrive on simplicity and scalability. Its elegance stems from a clever use of existing web standards, particularly HTTP. Understanding how REST APIs harness HTTP methods is not just a technical detail; it's the key to designing, consuming, and troubleshooting robust systems that speak a universal language. These verbs, GET, POST, PUT, DELETE, and their lesser-known counterparts, aren't just commands; they are a contract between client and server, orchestrating how data is retrieved, created, modified, and removed across the web.

Understanding REST API Methods: The Foundation of Web Communication

The web, at its core, is built on the Hypertext Transfer Protocol (HTTP). When you interact with a website or an application, you're constantly sending HTTP requests and receiving HTTP responses. REST (Representational State Transfer) is an architectural style that leverages HTTP as its communication protocol. It treats every piece of information as a "resource," and interaction with these resources happens through a standardized set of HTTP verbs, also known as rest api methods.

These methods define the type of operation you intend to perform on a resource identified by a URL (Uniform Resource Locator). By adhering to these standard methods, REST APIs achieve predictability, allowing developers to understand how to interact with an API without needing extensive custom documentation for every single endpoint. This standardization is a cornerstone of REST's success, enabling diverse clients and servers to communicate effectively.

The Role of HTTP Verbs in RESTful Design

In a RESTful architecture, resources are abstract entities that can be anything from a user profile to a product catalog item or a specific order. The URL identifies the resource, and the HTTP method describes the action to be performed on that resource. This clear separation of concerns, what resource (URL) and what action (HTTP method), is fundamental to REST's stateless and uniform interface constraints.

Choosing the right method is critical for building an intuitive and semantically correct API. Misusing methods can lead to confusion, unexpected behavior, and difficulties in caching, logging, and error handling. For instance, using a GET request to modify data would violate the principle of safety and could have unintended consequences if a client or intermediary assumes it's a read-only operation.

Let's delve into the core four HTTP methods GET, POST, PUT, and DELETE, which form the backbone of almost all rest api methods interactions, and then explore some other important methods.

The Core Four REST API Methods: GET, POST, PUT, DELETE

These four methods cover the fundamental operations (often referred to as CRUD: Create, Read, Update, Delete) that clients typically perform on server-side resources.

1. GET: Retrieving Resources

The GET method is used to retrieve data from a specified resource. It is arguably the most common HTTP method and forms the basis of fetching information from the web.

Purpose and Characteristics

• Purpose: To request a representation of the specified resource. GET requests should only retrieve data and have no other effect on the data.
• Safety: GET requests are considered "safe." This means they do not alter the state of the server or the resource. You can repeat a GET request multiple times without causing additional side effects (other than potentially consuming server resources like bandwidth or CPU cycles).
• Idempotency: GET requests are "idempotent." This means that making the same request multiple times will produce the same result (or resource representation) as making it once. The server's state remains unchanged.
• Caching: GET requests can be cached by browsers and other caching mechanisms, making them highly efficient for frequently accessed data.
• Body: GET requests should not contain a request body, as the parameters for retrieval are typically passed in the URL (query parameters) or as part of the path.

Examples

1. GET /api/products: Retrieves a list of all products.
2. GET /api/products/123: Retrieves the details of a specific product with ID 123.
3. GET /api/users?status=active&limit=10: Retrieves up to 10 active users, using query parameters for filtering and pagination.

When you navigate to a webpage in your browser, you are almost always initiating a GET request to retrieve the HTML, CSS, JavaScript, and images that make up that page. In a REST API, it's used to fetch data like user profiles, blog posts, product inventories, and more.

2. POST: Creating Resources

The POST method is used to submit an entity to the specified resource, often causing a change in state or the creation of a new resource on the server.

Purpose and Characteristics

• Purpose: To send data to the server to create a new resource or to perform an action that isn't easily mapped to other HTTP methods.
• Safety: POST requests are not "safe." They are intended to cause changes on the server, such as creating a new entry in a database.
• Idempotency: POST requests are typically not "idempotent." Making the same POST request multiple times could result in multiple new resources being created (e.g., submitting an order form twice might create two orders). Clients must be careful when retrying POST requests.
• Caching: POST requests are generally not cacheable by default, although certain conditions might allow it.
• Body: POST requests typically send data in the request body (e.g., JSON, XML, form data) which contains the information needed to create the new resource.

Examples

1. POST /api/users with a JSON body {"name": "Alice", "email": "alice@example.com"}: Creates a new user. The server will typically respond with a 201 Created status code and the URL of the newly created resource.
2. POST /api/products/123/reviews with a JSON body {"rating": 5, "comment": "Great product!"}: Adds a new review to product 123.

POST is often used when a client is submitting data, such as signing up for an account, submitting a form, or adding an item to a shopping cart.

3. PUT: Updating/Replacing Resources

The PUT method is used to update an existing resource or create a new resource at a specified URI if it does not already exist.

Purpose and Characteristics

• Purpose: To replace all current representations of the target resource with the uploaded content. If the resource identified by the URI does not exist, PUT can create it.
• Safety: PUT requests are not "safe" as they modify server state.
• Idempotency: PUT requests are "idempotent." Sending the exact same PUT request multiple times will result in the same resource state on the server as sending it once. Even if a new resource is created on the first request, subsequent identical requests to the same URI will simply update that same resource.
• Caching: PUT requests are generally not cacheable.
• Body: PUT requests typically include the complete representation of the resource in the request body.

Examples

1. PUT /api/products/123 with a JSON body {"name": "Updated Product", "price": 29.99}: Updates all details of product 123. If product 123 didn't exist, this might create it.
2. PUT /api/users/456 with a JSON body {"firstName": "Jane", "lastName": "Doe"}: Replaces the entire user resource for ID 456 with the provided data.

The key distinction between PUT and POST for updates is idempotency and the client's role in specifying the resource's URI. With PUT, the client typically provides the complete new state of the resource and specifies the exact URI. With POST, the server usually decides the URI of the newly created resource.

4. DELETE: Removing Resources

The DELETE method is used to remove the specified resource.

Purpose and Characteristics

• Purpose: To request that the origin server delete the resource identified by the Request-URI.
• Safety: DELETE requests are not "safe" as they modify server state.
• Idempotency: DELETE requests are "idempotent." Deleting a resource multiple times has the same effect as deleting it once (the resource is either gone or doesn't exist after the first successful deletion).
• Caching: DELETE requests are generally not cacheable.
• Body: DELETE requests should not contain a request body, although some servers might ignore it if present.

Examples

1. DELETE /api/products/123: Deletes the product with ID 123.
2. DELETE /api/users/456: Removes the user with ID 456.

A successful DELETE request typically returns a 204 No Content status code (if no body is returned) or 200 OK with a status message or description of the deletion. It's a straightforward method for resource removal.

Beyond the Core: Other Important REST API Methods

While GET, POST, PUT, and DELETE are the most frequently used rest api methods, HTTP defines several others that offer more specialized functionality. Understanding these can help you design more precise and efficient APIs.

1. PATCH: Partially Updating Resources

The PATCH method is used to apply partial modifications to a resource.

Purpose and Characteristics

• Purpose: To apply a partial update to a resource. Unlike PUT, which requires the entire resource representation, PATCH allows you to send only the data fields that need to be changed.
• Safety: PATCH requests are not "safe."
• Idempotency: PATCH requests are generally not inherently idempotent. Whether a PATCH request is idempotent depends on how the server implements the patching logic. For instance, an operation like "increment quantity by 1" is not idempotent, while "set quantity to 5" is. The API documentation should clarify this.
• Body: PATCH requests require a request body detailing the changes, often in a specific patch format like JSON Patch or JSON Merge Patch.

Example

• PATCH /api/products/123 with a JSON body {"price": 35.00}: Updates only the price of product 123, leaving other fields unchanged.

PATCH is highly useful for large resources where sending the entire object for a minor update would be inefficient.

2. HEAD: Fetching Headers

The HEAD method is identical to GET, but it asks for a response without the response body. It only retrieves the header information.

Purpose and Characteristics

• Purpose: To retrieve metadata about a resource without transferring the resource itself. This is useful for checking if a resource exists, determining its size, or verifying if it has been modified (using ETag or Last-Modified headers) before making a full GET request.
• Safety: HEAD requests are "safe."
• Idempotency: HEAD requests are "idempotent."
• Body: HEAD requests should not have a body, and the response will never have a body.

Example

• HEAD /api/large-file.zip: Checks the Content-Length header to see the file size before deciding to download it with a GET request.

3. OPTIONS: Discovering Supported Methods

The OPTIONS method is used to describe the communication options for the target resource.

Purpose and Characteristics

• Purpose: To allow a client to discover which HTTP methods (GET, POST, PUT, DELETE, etc.) are supported by a server for a specific URL or resource. This is often used in cross-origin resource sharing (CORS) preflight requests.
• Safety: OPTIONS requests are "safe."
• Idempotency: OPTIONS requests are "idempotent."
• Body: OPTIONS requests typically have no body, and the response usually contains an Allow header listing the supported methods.

Example

• OPTIONS /api/products/123: A response might include an Allow: GET, PUT, DELETE header, indicating that you can retrieve, update, or delete product 123.

Idempotency and Safety: Why They Matter

These two concepts are fundamental to understanding the behavior of rest api methods and building robust, predictable systems.

1. Safety

An HTTP method is "safe" if it doesn't cause any server-side state changes when executed. In other words, safe methods are read-only operations. You can invoke them repeatedly without worrying about unintended consequences on the server's data.

• Safe Methods: GET, HEAD, OPTIONS
• Non-Safe Methods: POST, PUT, DELETE, PATCH

The primary benefit of safe methods is that they can be invoked automatically by browsers (e.g., when clicking a link or refreshing a page) or by intermediaries (like caches or proxies) without fear of causing harm. For instance, if a network error occurs during a GET request, the client can safely retry it without knowing whether the first attempt succeeded or failed.

2. Idempotency

An HTTP method is "idempotent" if performing the same request multiple times has the same effect on the server as performing it once. The important part is the "effect on the server," not necessarily the response from the server. The response might differ (e.g., a 200 OK on the first delete, and a 404 Not Found on subsequent attempts), but the resource state on the server should be consistent.

• Idempotent Methods: GET, HEAD, PUT, DELETE, OPTIONS
• Non-Idempotent Methods: POST (typically), PATCH (depends on implementation)

Idempotency is crucial for fault tolerance. If a client sends an idempotent request and doesn't receive a response (due to network issues, for example), it can safely retry the request without concern that it will inadvertently create duplicate resources or corrupt data. For example, retrying a DELETE request will still result in the resource being deleted, even if the first attempt succeeded.

Statelessness in REST: How Methods Fit In

One of the fundamental constraints of REST is statelessness. This means that each request from a client to a server must contain all the information needed to understand the request. The server should not store any client context between requests. Every request is treated as independent.

The rest api methods contribute to this statelessness by providing a clear and self-contained definition of the action. When a client sends a GET request, all parameters needed to retrieve the resource are in the URL. For a POST or PUT, the necessary data is in the request body. The server doesn't need to remember anything about previous interactions with that client to process the current request correctly.

This stateless nature offers several benefits:

• Scalability: Servers don't need to dedicate resources to maintaining session state, making it easier to scale by adding more servers.
• Reliability: If a server fails, another server can pick up the request without loss of context.
• Visibility: Each request can be understood in isolation, simplifying debugging and monitoring.

Designing RESTful APIs with Methods: Best Practices

Properly using rest api methods is central to building effective and maintainable RESTful APIs.

1. Choosing the Right Method

Always select the HTTP method that best describes the intended action on the resource:

• Use GET for fetching data.
• Use POST for creating new resources or for operations that are not idempotent.
• Use PUT for completely replacing a resource at a known URI, or for creating a resource if the client dictates its URI.
• Use PATCH for partial updates when only a subset of a resource's fields needs to be modified.
• Use DELETE for removing a resource.

2. Error Handling with HTTP Status Codes

HTTP status codes are essential for communicating the outcome of an API request. Combine them appropriately with rest api methods:

• 200 OK: General success for GET, PUT, PATCH, DELETE (if content is returned).
• 201 Created: Resource successfully created (common for POST). The response should include a Location header pointing to the new resource.
• 204 No Content: Request successful, but no content to return (common for DELETE, PUT, or POST if no resource representation is needed).
• 400 Bad Request: Client error, often due to invalid input data.
• 401 Unauthorized: Authentication required or failed.
• 403 Forbidden: Client does not have permission to access the resource.
• 404 Not Found: The requested resource does not exist.
• 405 Method Not Allowed: The HTTP method used is not supported for the requested resource (e.g., trying to POST to a read-only endpoint).
• 409 Conflict: Request could not be completed due to a conflict with the current state of the resource (e.g., trying to create a resource that already exists with a unique identifier).
• 500 Internal Server Error: General server-side error.

3. Resource Naming Conventions

While not directly about methods, consistent resource naming complements the use of HTTP methods. Always use plural nouns for collections and singular nouns for specific resource instances:

• /users (collection)
• /users/123 (specific user)
• /products/456/reviews (sub-collection of reviews for a product)

Avoid verbs in resource names (e.g., /getAllUsers or /createUser), as the HTTP method itself should convey the action.

Real-World Examples and Use Cases

Let's consider a simple e-commerce API to illustrate how these rest api methods work together:

1. Scenario: Managing Products

1. Fetching All Products:
   GET /products (Returns a list of all products)
2. Fetching a Specific Product:
   GET /products/PROD001 (Returns details for product PROD001)
3. Creating a New Product:
   POST /products
   Body: {"name": "New Widget", "description": "A fantastic new gadget", "price": 99.99}
   Response: 201 Created, with Location: /products/PROD002
4. Updating an Entire Product:
   PUT /products/PROD002
   Body: {"name": "Updated Widget Name", "description": "The best widget ever", "price": 109.99, "stock": 50} (replaces all fields for PROD002)
5. Partially Updating a Product:
   PATCH /products/PROD002
   Body: {"price": 89.99} (only updates the price for PROD002)
6. Deleting a Product:
   DELETE /products/PROD001
   Response: 204 No Content

2. Scenario: User Authentication (Non-Resourceful Action)

While most actions map to resources, some "actions" don't fit perfectly. User login is a classic example. It's not creating a "session resource" in the traditional sense, but rather performing an action.

• Logging In:
  POST /login
  Body: {"username": "myuser", "password": "mypassword"}
  Response: 200 OK with an authentication token (e.g., JWT)

Here, POST is appropriate because it's a non-idempotent operation that changes server state (creating a session or issuing a token) and doesn't correspond to creating a new resource under a client-specified URI.

Common Pitfalls and How to Avoid Them

Even with clear guidelines, developers sometimes make mistakes when implementing rest api methods.

Misusing GET for State Changes

• Pitfall: Using GET /api/users/123/activate to activate a user. This violates the "safety" principle of GET.
• Avoidance: For actions that change state, always use POST, PUT, or DELETE. A better approach would be POST /api/users/123/activation or PATCH /api/users/123 with a body like {"status": "active"}.

Not Distinguishing Between PUT and PATCH

• Pitfall: Using PUT for partial updates, or always requiring the full resource even for minor changes.
• Avoidance: Use PUT when the client is sending the complete, new representation of the resource. Use PATCH when the client is sending only the changes needed for a partial update. Ensure your API clearly documents which method expects what kind of payload.

Inconsistent Use of Status Codes

• Pitfall: Always returning 200 OK even for errors, or using custom error codes in the response body without appropriate HTTP status codes.
• Avoidance: Adhere strictly to HTTP status code semantics. A 404 Not Found is much more informative than a 200 OK with an "error" field in the JSON body, especially for automated clients and intermediaries.

Violating Idempotency with POST (When Not Intended)

• Pitfall: Allowing multiple identical POST requests to create duplicate resources, especially if a client retries due to network timeout.
• Avoidance: Implement mechanisms like unique client-generated request IDs (idempotency keys) for critical POST operations, allowing the server to recognize and safely ignore duplicate requests within a certain timeframe. Or, consider if PUT might be a more appropriate method if the client controls the resource identifier.

Lack of Proper Authentication and Authorization

• Pitfall: Not securing endpoints adequately, allowing unauthorized access or modification.
• Avoidance: Implement robust authentication (e.g., OAuth2, API Keys, JWTs) and authorization (role-based access control) for all sensitive rest api methods, especially POST, PUT, PATCH, and DELETE. Return 401 Unauthorized or 403 Forbidden as appropriate.

Conclusion

The HTTP methods, GET, POST, PUT, DELETE, and others are the fundamental verbs in the language of RESTful APIs. They provide a clear, standardized contract for how clients and servers interact with resources, defining actions that are both intuitive and predictable. By understanding their purpose, characteristics like safety and idempotency, and best practices for their application, developers can craft APIs that are not only functional but also robust, scalable, and easy to consume. Adhering to these principles ensures that your API contributes to a more coherent and efficient web, fostering seamless integration and reliable data exchange across the ever-expanding digital ecosystem. Mastering these rest api methods is a cornerstone of modern web development, empowering you to build powerful applications that stand the test of time.

FAQs

1. What are the main REST API methods?

The four main REST API methods are GET, POST, PUT, and DELETE. GET retrieves data, POST creates new resources, PUT updates or replaces existing resources, and DELETE removes resources. These methods correspond to the basic CRUD (Create, Read, Update, Delete) operations.

2. What is the difference between PUT and PATCH?

PUT is used to completely replace a resource with the data provided in the request body. If the resource doesn't exist, PUT can create it at the specified URI. PATCH, on the other hand, is used for partial updates, applying only the changes specified in the request body to modify specific fields of a resource without sending its entire representation.

3. What does it mean for an HTTP method to be "idempotent"?

An HTTP method is idempotent if making the same request multiple times has the same effect on the server as making it once. The server's state after one request is identical to its state after many identical requests. GET, PUT, DELETE, and HEAD are idempotent, while POST is typically not.

4. Why should I not use GET for actions that change server state?

GET requests are considered "safe" methods, meaning they should not cause any side effects or change the state of the server. Using GET for state-changing actions violates this principle, can lead to unexpected behavior (e.g., unintended changes by web crawlers or caching mechanisms), and makes debugging more difficult. POST, PUT, or DELETE should be used for operations that modify data.

5. What HTTP status code should I return for a successful resource creation?

For a successful resource creation using a POST request, the standard HTTP status code to return is 201 Created. It should ideally be accompanied by a Location header in the response, which provides the URL of the newly created resource.