What is an HTTP status code?

An HTTP status code (HTTP response code) is a numeric code in the HTTP response that shows how the server finished processing the request.

In simple terms: an HTTP status code is the short result of a request: success, an error, or something else.

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#Why HTTP codes are needed

HTTP codes are needed so a client (browser, application):

• understands whether the request succeeded
• learns why an error occurred
• knows what to do next (retry the request, show an error, go to another address)

Without codes, the client would have to guess what happened.

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#Where the HTTP status code is located

An HTTP code:

• is sent in the HTTP response
• is located in the first line of the response

Example:

HTTP/1.1 200 OK

Here:

• 200 is the status code
• OK is the text explanation

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#Main groups of HTTP codes

HTTP codes are divided into classes by their first digit:

#2xx, Success

The request was completed successfully.

• 200 OK - everything is fine
• 201 Created - the resource was created

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#3xx, Redirection

The client needs to go to another address.

• 301 Moved Permanently
• 302 Found

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#4xx, Client error

A problem with the request.

• 400 Bad Request - an invalid request
• 401 Unauthorized - authorization is required
• 403 Forbidden - access is denied
• 404 Not Found - the resource was not found

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#5xx, Server error

The server received a correct request but could not process it.

• 500 Internal Server Error
• 502 Bad Gateway
• 503 Service Unavailable

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#An important point for an interview

• 404 is a normal HTTP response, not "the server crashed"
• 4xx → an error on the client's side
• 5xx → an error on the server's side

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#Real-life example

You ask:

"Give me the page"

The server responds:

• 200 → "Here is the page"
• 404 → "No such page exists"
• 500 → "I'm broken, try again later"

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#Short answer for an interview

Remember this wording:

An HTTP status code is a numeric code in the HTTP response that shows the result of processing the request and reports whether it succeeded or an error occurred.