HTTP status codes are a crucial part of the World Wide Web, as they provide important information about the status of a given HTTP request. These codes are sent back to the client from the server in response to a request, and they indicate whether the request was successful, or if there was an error.
There are many different HTTP status codes, each with its own specific meaning. For example, the code 200 indicates that a request was successful, while the code 404 indicates that the requested resource could not be found. Other codes include 301for a permanent redirect, “403” for a forbidden request, and 500 for a server error.
One of the most important things to understand about HTTP status codes is that they help to provide more detailed information about a given request. This can be particularly useful for troubleshooting, as it can help to identify where a problem might be occurring in the communication between a client and a server.
200 Series Status Codes
One of the most commonly seen HTTP status codes is the 200 series. These codes indicate that a request was successful, and that the requested information has been returned to the client. For example, a 200 OK status means that the request was received and understood, and the requested resource has been returned.
200 - OK
The first status code is 200 and is just a generic success status. All this says is that request was received and understood, and the requested resource has been returned but it doesn’t give any more information than that. Because of this, the 200 status is the fallback status you should use for any successful request when there is no more specific code to use instead.
201 - Created
Speaking of more specific codes, we have the 201 code. This is a success code that says a resource was successfully created. Most often you will see this as the result of a POST request since most POST requests are used for creating things. For example, if you have an API route for creating a new entry in your DB you should return a 201 if that entry was created successfully.
202 - Accepted
The 202 status code is a bit niche. Essentially, this code just means that the response was successfully received, but that the actual action of the request (creating a resource, updating data, etc.) has not been completed yet. This is commonly used when doing a particular task is very slow so it gets queued up to do later. For example, if you need to generate a large report that you will later email to a user then you may return a 202 to let the client know you are processing the request but have not finished it yet.
204 - No Content
Another specific code is the 204 code which means the request was successful, but there is no data to return. This is very common with DELETE requests since there is usually no data to return as a response to deleting something. The biggest key to this status code is that it cannot contain any data in the body.
300 Series Status Codes
Another commonly seen series is the 300 series, which indicates that the requested resource has been moved or redirected. For example, a 301 Moved Permanently status indicates that the resource has been permanently moved to a new location, and any future requests should be directed to the new location.
301 - Moved Permanently
Probably the most common type of 300 series status code is the 301. This just says that the resource has been permanently moved to a new location, and any future requests should be directed to the new location. This new URL must be sent down in the response with the 301 code. If this happens the browser will automatically redirect users to the new URL. This will also trigger search engines to associate all data from the old URL with the new URL so you shouldn’t lose any rankings in a search engine by doing this.
302 - Found
Similar to the 301 status this status is used to tell the client that the page is at a new URL but this is a temporary change. This means that search engines won’t replace the old URL with this new URL. This is useful if you need to send a user to a different version of the same page, but don’t want that version of the page to replace your main version in search engines. For example, if you are doing A/B tests you would 302 redirect half your users to the alternate version of the site. This is also useful for things like localization where you may want to redirect users to localized versions of your site based on where they are from.
304 - Not Modified
The final important 300 series status code is the 304. This is used for caching and essentially just says that the resource being requested has not changed. This needs to be used in conjunction with a previous 200 status request that included caching headers such as the Cache-Control, and Expires header. When a client tries to access a resource before the cached time period has expired the server will return a 304 to prevent having to retransmit all the data to the client.
400 Series Status Codes
The 400 series of HTTP status codes indicates that there was an error with the request made by the client. This could be due to a malformed request, missing parameters, or other issues. For example, a 404 Not Found status indicates that the requested resource could not be found on the server.
400 - Bad Request
Similar to the 200 status code, the 400 status code represents a generic bad request. This just means that data being sent to the request (URL params, JSON, etc.) is incorrect, malformed, missing, or in some way unusable by the server. This is the default status message to send back when you have a request that cannot be handled due to the client. For example, if you try to send a request to create a new user but don’t pass a name the server will send a 400 status code to let you know the name field is required.
401 - Unauthorized
The 401 status code is a bit confusing since while it uses the word unauthorized (which means you don’t have permission) this status code actually means you are unauthenticated. The main difference here is that being unauthenticated means you are not logged in or attempted to log in with invalid credentials. This can happen if you pass along an invalid API key or no API key at all when dealing with APIs.
403 - Forbidden
When dealing with permissions you should use the 403 status code. This status informs the client that they do not have permission to perform this request. This should only be returned if the client is sending along valid credentials (such as a valid API key), but lack the permissions to do the action. For example, if a basic user tries to access admin data you would return a 403.
404 - Not Found
This is the most common HTTP status code people are aware of and it just means the resource could not be found. This could be used for example if you try to access a URL that does not exist or if you try to access something from the database that does not exist.
429 - Too Many Requests
The final important 400 series status code is 429. This code is used when dealing with rate limiting. For example, if you only allow users to access your API 30 times per minute and someone tries to access it 31 times you would return a 429 status code to let them know they need to wait to send their next request. This also must have a Retry-After HTTP header with the amount of time to wait before requests will be accepted by the API.
500 Series Status Codes
Finally, the 500 series of HTTP status codes indicates an error on the server side. This could be due to a server malfunction, a misconfigured server, or other issues. For example, a 500 Internal Server Error indicates that the server encountered an unexpected condition and was unable to complete the request.
500 - Internal Server Error
By far the most common 500 series code is 500. This code just informs the client there was some form of error on the server. This error could be due to anything from an error in the code leading to the program crashing (even if this error is caused by bad client data), to problems accessing the database. This should be used in any situation where the server has an error and there is no more specific code that is applicable.
503 - Service Unavailable
There aren’t too many other 500 series status codes you will use, but 503 is somewhat common. This status code just means that the server is not able to handle the request. This is common to use when doing some form of planned server maintenance where the server is down while being updated. This should also include a Retry-After HTTP header with the estimated time until the server will be back up.
Conclusion
In addition to providing useful information for troubleshooting, HTTP status codes are also important for optimizing the performance of a website. By understanding the different codes and their meanings, web developers can ensure that their site is returning the appropriate status codes for each request, which can help to improve the user experience and increase the overall efficiency of the site.
Overall, HTTP status codes are an essential part of the web, and they play a vital role in helping to ensure that communication between clients and servers is smooth and efficient. By understanding the different codes and their meanings, we can better understand how the web works, and how to optimize the performance of our own websites.