HTTP Status Codes Reference Cheat Sheet

A printable reference covering HTTP basics, request methods, status code classes, common response codes, and troubleshooting patterns for grades 9-12.

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HTTP status codes are three-digit numbers that a web server sends back after a browser, app, or API client makes a request. They tell whether the request succeeded, failed, redirected, or needs more action. This cheat sheet helps students read web responses, debug API calls, and understand how websites communicate. It is especially useful for web development, networking, and cybersecurity basics.

Key Facts

HTTP status codes are grouped by first digit: 1xx informational, 2xx success, 3xx redirection, 4xx client error, and 5xx server error.
GET requests ask for data from a server and should not change server data.
POST requests send data to a server, often to create a new resource or submit a form.
PUT usually replaces an entire resource, while PATCH usually updates part of a resource.
200 OK means the request succeeded and the server returned the expected response.
201 Created means the request succeeded and a new resource was created.
404 Not Found means the requested resource does not exist at the given URL.
500 Internal Server Error means something went wrong on the server while processing the request.

Vocabulary

HTTP: HTTP is the protocol that browsers, apps, and servers use to request and send web data.
Status Code: A status code is a three-digit server response that summarizes the result of an HTTP request.
Client: A client is the browser, app, or program that sends a request to a server.
Server: A server is the computer or service that receives requests and sends back responses.
Redirect: A redirect tells the client to look for the requested resource at a different URL.
API: An API is a set of rules that lets programs request data or actions from another software system.

Common Mistakes to Avoid

Confusing 404 and 500 is wrong because 404 means the client requested a missing resource, while 500 means the server failed while handling the request.
Using GET to change data is wrong because GET should be safe and should only retrieve information, not create, update, or delete it.
Treating every 3xx code as an error is wrong because 3xx responses usually mean the client should follow a different URL.
Assuming 401 and 403 mean the same thing is wrong because 401 usually means authentication is needed, while 403 means access is forbidden even if the server understands the user.
Ignoring the request method when debugging is wrong because the same URL can return different results for GET, POST, PUT, PATCH, or DELETE.

Practice Questions

1 A browser requests /images/logo.png, but the file does not exist. Which status code class and specific common code should the server return?
2 An API request successfully creates a new user account. Which status code is more appropriate: 200 OK or 201 Created?
3 A student sends a POST request to /login with the wrong password and receives 401. What does the first digit tell you about the type of problem?
4 Why can a 500 Internal Server Error still happen even if the client typed the correct URL and used the correct HTTP method?

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