Understanding the Key Differences Between HTTP GET and POST Requests

Overview

GET and POST are two of the eight HTTP request methods. They are defined by the HTTP protocol, which runs on top of TCP/IP.

HTTP Request Message Structure

An HTTP request consists of three parts:

Request line : method, URL, and HTTP version (e.g., GET /path HTTP/1.1).

Request headers : zero or more header fields, each in the form Header-Name: value, terminated by CRLF.

Request body : optional data sent after an empty line; used by methods such as POST.

GET Request Example

The following request was captured when accessing https://api.github.com/search/users?q=JakeWharton:

GET /search/users?q=JakeWharton HTTP/1.1
Host: api.github.com
Connection: keep-alive
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.86 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9
Cookie: _octo=GH1.1.1623908978.1549006668; _ga=GA1.2.548087391.1549006688; logged_in=yes; dotcom_user=GoMarck; _gid=GA1.2.17634150.1554639136; _gat=1

The request line shows the method GET, the URL with query parameters, and HTTP/1.1. All subsequent lines are headers; there is no request body.

Characteristics of GET

Data is placed in the URL after a ? and parameters are joined with &.

According to the HTTP specification, GET is used for information retrieval and should be safe and idempotent.

GET responses can be cached by browsers; identical subsequent requests may be served from cache.

The URL length is limited by browsers and servers, not by the HTTP specification itself.

GET typically generates a single TCP packet that carries both headers and (non‑existent) body.

POST Request Example

POST / HTTP/1.1
Host: www.wrox.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.6) Gecko/20050225 Firefox/1.0.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 40
Connection: Keep-Alive

name=Professional%20Ajax&publisher=Wiley

Here the request line uses the method POST. The request body follows a blank line and contains the form data name=Professional%20Ajax&publisher=Wiley.

Characteristics of POST

POST is intended for operations that may modify server resources (e.g., submitting a like on Zhihu).

Because it can change server state, POST is neither safe nor idempotent.

Request data resides in the body, so POST does not inherit the URL length limits of GET.

POST typically involves two TCP packets: one for headers, then after a 100 Continue response, a second packet for the body.

Why HTTP Distinguishes GET and POST

Even though both methods ultimately use TCP, the HTTP protocol assigns distinct semantics to aid management and routing. GET is defined for pure retrieval, while POST is defined for actions that may modify resources. This separation allows servers, proxies, and browsers to apply different handling rules, such as caching policies and safety checks.

Conclusion

At the transport layer, GET and POST are both TCP connections, but HTTP gives them separate categories to express intent, enforce safety and idempotence rules, and control how request data is transmitted. Understanding these differences helps developers choose the appropriate method for a given operation.