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HTTP methods help developers define how clients and servers communicate over the web. They describe how data is sent, received, updated, or deleted in APIs and web applications.

In this article, you’ll learn what each HTTP method does, when to use it, and how to avoid common mistakes.

What are HTTP Methods?

HTTP stands for Hypertext Transfer Protocol. It is the communication protocol used between clients (like browsers or apps) and servers to exchange data over the internet. HTTP defines how requests are made and how responses are returned.

When a client sends a request to a server, it uses an HTTP method to specify the action it wants to perform on a resource. Each method carries constraints and guarantees, such as safety and idempotency, that shape how APIs behave in distributed systems.

Structure of an HTTP Request

An HTTP request consists of several key parts:

• Request Line: Contains the HTTP method (e.g., GET, POST), the URL of the resource being requested, and the HTTP version (e.g., HTTP/1.1). This line tells the server what action the client wants to perform.
• Headers: These carry metadata about the request and provide the server with important context to process the request correctly. This includes:
  • Content types the client can accept (Accept header)
  • Authentication credentials (Authorization header)
  • Caching rules (Cache-Control, If-Modified-Since)
  • Other information like user-agent, language preferences, etc.
• Body (Optional): Contains the data sent to the server, typically included with methods that create or update resources like POST, PUT, and PATCH. This part delivers the actual content or instructions the client wants the server to handle.

The server uses all this information to process the request correctly and respond accordingly.

List of HTTP Methods

Below is an in-depth look at each HTTP method, explaining its purpose, characteristics, and typical server responses.

1. GET Method

The GET method retrieves data from the server without modifying any resources. It is safe and idempotent. Because it only fetches data, browsers or proxies can cache and pre-fetch it to improve performance. GET requests do not usually include a request body.

Expected server responses include:

• 200 OK: The resource does not exist, so no headers are returned.
• 304 Not Modified: The resource has not changed since the last request, based on caching headers.

2. POST Method

The POST method sends data to the server to create a new resource or execute operations. It is neither safe nor idempotent, meaning repeated identical POST requests can result in multiple resources or repeated actions. POST requests usually include a body with the data to submit.

Expected server responses include:

• 201 Created: Returned when a new resource has been successfully created on the server.
• 204 No Content: The request succeeded without returning any content.
• 200 OK: Returned when the server successfully processes the request and sends back the requested data.

3. PUT Method

The PUT method replaces or creates the resource at the specified URL using the data in the request body. It is idempotent but unsafe. Sending the same PUT request multiple times results in the same final resource state without creating duplicates. PUT requires the client to send the complete representation of the resource to be stored.

Expected server responses include:

• 200 OK or 204 No Content: Resource was updated successfully.
• 201 Created: Resource was created if it did not exist.

4. PATCH Method

PATCH partially modifies a resource using the changes described in the request body. Its idempotency depends on the operation: operations that replace values are idempotent, while those that increment or append are not.

Expected server responses include:

• 200 OK or 204 No Content: The resource was successfully updated.
• 404 Not Found: The target resource does not exist.

5. DELETE Method

The DELETE method requests the removal of the resource identified by the URL. It is unsafe but idempotent, so repeated identical DELETE requests have the same effect as a single one. Servers usually implement authorization and validation to prevent accidental deletions.

Expected server responses include:

• 200 OK: Resource deleted successfully with optional response body.
• 204 No Content: Resource deleted, no content returned.
• 404 Not Found: Resource was not found or already deleted.

6. HEAD Method

HEAD is similar to GET but requests only the headers without the response body. It is safe and idempotent. HEAD is often used to check if a resource exists or to retrieve metadata like content type or length without transferring the resource itself.

Expected server responses include:

• 200 OK: The resource exists, headers are returned, and the body is intentionally omitted.
• 404 Not Found: The resource does not exist, so no headers are returned.

7. OPTIONS Method

OPTIONS requests information about the communication options available for the target resource. It is safe and idempotent. OPTIONS is commonly used for CORS preflight checks and to discover supported HTTP methods on a server.

Expected server responses include:

• 200 OK: Response contains allowed methods and other options in headers.
• 204 No Content: No content was returned, but options information was provided in the headers.

8. CONNECT Method

CONNECT establishes a tunnel to the server identified by the target resource. It is mainly used to facilitate SSL-encrypted connections through a proxy. CONNECT is unsafe and not idempotent, as it creates a new network connection.

Expected server responses include:

• 200 OK: The tunnel was established successfully.
• 502 Bad Gateway: The proxy failed to connect to the target server.

9. TRACE Method

TRACE performs a message loop-back test along the path to the target resource. It is safe and idempotent, but it is rarely used because it can expose security risks like cross-site tracing attacks.

Expected server responses include:

• 200 OK: The server echoes the received request in the response body.
• 405 Method Not Allowed: The server does not allow TRACE requests.

Comparison of HTTP Methods

HTTP methods differ in safety, idempotency, request body usage, and typical responses. This table summarizes their key attributes for accurate API design and implementation.

Safe vs. Unsafe HTTP Methods

In HTTP, a method is considered safe if it does not change any data or state on the server. Safe methods only retrieve information without causing side effects. Because of this, they can be repeated or called automatically without risk. Standard safe methods include GET and HEAD.

On the other hand, unsafe methods can modify data or server state. These include POST, PUT, PATCH, and DELETE. Using unsafe methods requires caution because repeated requests may change data multiple times, potentially causing errors or security risks.

Browsers and tools rely on it to decide when they can safely retry requests or prefetch links to speed up the user experience. For example, browsers may prefetch GET requests to load pages faster, but avoid prefetching POST or DELETE requests because they can alter data.

Understanding Idempotent Methods

An HTTP method is idempotent if sending the same request multiple times results in the same server state as sending it once. This is important in systems where requests may be retried due to network issues or timeouts.

Idempotency does not mean the method is safe. For example, DELETE is idempotent because deleting the same resource multiple times has the same effect as deleting it once. However, DELETE still changes the server state, so it is unsafe.

Moreover, idempotent methods help prevent unintended side effects from repeated requests. Common idempotent methods include GET, PUT, DELETE, and HEAD.

Thus, APIs need to clearly define the idempotency of their methods so clients can reliably handle retries and concurrent requests.

Common Mistakes When Using HTTP Methods

Developers new to RESTful API design often struggle with properly using HTTP methods. Misusing these methods can lead to APIs that are confusing, insecure, or difficult to maintain. Below are some frequent errors to avoid:

1. Overusing POST for All Requests

Beginners sometimes use POST for every request, even when retrieving or deleting data. This practice hides the operation’s intent and can prevent clients and intermediaries from optimizing requests.

Incorrect:

Correct:

Using the correct methods helps clarify API behavior and supports features like caching.

2. Mixing Up PUT and PATCH Usage

A common source of confusion is when to use PUT versus PATCH. PUT should replace the entire resource, while PATCH applies partial updates.

Incorrect:

Correct:

A clear distinction ensures updates are predictable and prevent unintended overwrites.

3. Neglecting Idempotency Rules

Idempotency means that sending the same request multiple times should have the same effect as sending it once. Using non-idempotent methods like POST for operations that need to be idempotent can cause issues, especially if retries occur.

Incorrect:

Correct:

Adhering to idempotency improves reliability in distributed systems.

4. Using GET for Actions That Change Data

GET requests should only fetch data without side effects. Using GET to perform updates or deletions breaks HTTP standards and can cause unexpected behavior.

Incorrect:

Correct:

Using GET only for safe operations helps caching work correctly and prevents unintended data changes or security risks.

Best Practices for Using HTTP Methods in REST APIs

Using HTTP methods correctly ensures your REST API is reliable, predictable, and easy to maintain. Follow these guidelines to design APIs that behave as expected across diverse clients and use cases:

• Use nouns in paths: Endpoints should represent resources (like /users, /orders) rather than actions. The HTTP method conveys the intended action, keeping URLs clean and RESTful.
• Match methods to CRUD: Use GET to read data, POST to create, PUT or PATCH to update, and DELETE to remove resources. Avoid using POST for all operations to maintain clarity and enable proper caching and idempotency handling.
• Maintain idempotency: Design PUT and DELETE requests to be idempotent. Repeated requests should not cause unintended side effects or inconsistent data. PATCH requests should be carefully implemented to either be idempotent or clearly documented if not.
• Use correct status codes: Return status codes that reflect the outcome accurately. For example, use 201 Created after successful resource creation, 204 No Content when an update succeeds without returning data, and 404 Not Found when a resource does not exist.
• Support filtering and pagination: To handle large data sets efficiently, support query parameters for filtering results, sorting order, and paginating responses. This improves performance and user experience.
• Use caching headers: Properly configure the Cache-Control, ETag, and Last-Modified headers on GET responses to enable client and proxy caching, reducing server load and improving response times.
• Validate and authenticate: Always validate data sent by clients to prevent injection attacks or invalid states. Use authentication and authorization headers to protect sensitive endpoints.
• Version your API: Include version information in your URL or headers to support backward compatibility and smooth upgrades without breaking existing clients.
• Provide documentation: Clearly document which HTTP methods are supported on each endpoint, expected request and response formats, status codes, and any special behavior like idempotency or side effects. Good documentation reduces integration errors and supports faster adoption.

How Requestly Helps With HTTP Method Testing

Requestly helps you test, debug, and modify HTTP requests easily without changing backend code. It lets you create rules to intercept and change request methods, headers, URLs, or responses. This helps you test APIs under different scenarios, simulate errors, or debug client-server communication.

With Requestly, you can:

• Modify HTTP methods on the fly to test how servers respond to different requests.
• Add, remove, or change headers to test authentication, caching, or content negotiation.
• Redirect requests to mock servers or alternate endpoints for testing purposes.
• Simulate slow networks or errors to check app behavior in adverse conditions.
• Automate repetitive testing tasks to save time and improve accuracy.

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Conclusion

HTTP methods define the actions clients perform on server resources. They include GET to retrieve data, POST to submit new data, PUT to update existing resources fully, PATCH to update them, and DELETE to remove resources partially. Each method governs how clients communicate their intentions to the server and how the server processes those requests.

Testing and debugging these requests is essential to ensure APIs behave correctly. Requestly helps developers redirect requests to test alternate endpoints, modify HTTP Headers to test how APIs respond to different header values, and Insert Custom Scripts to simulate various HTTP methods during development.

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