Browsing the web can sometimes make you think some secret agency is controlling the errors and how they are displayed. Most everyone knows that a 404 error means that the file cannot be found. In other words, if you go to a website and try to bring up a particular page that has been removed, or never existed to begin with, you get that glorious 404 error.

But what about all the other cryptic codes? There are tons of them and most of them are in the 300, 400 and 500 range. Here’s a quick list of the most common ones and a brief explanation of each code:

2xx – Everything is Good to Go!

You likely won’t see these codes displayed in your browser, but the web developer nerds love to see them.

• 200 OK – Success! This means the page is found and loads up just fine. You’ll likely never see this code on your screen, but web developers and server admins love to see this one in the logs.
• 201 Created – Means a new resource was created. Shazam!
• 204 No Content – Everything is working, but the file doesn’t have anything to serve up to the user.

3xx – Redirect

Things change and websites sometimes need to move to a new zip code.

• 301 Moved Permanently – The website has permanently moved to a new address. Time to update the web link for the bookmark you may have of this website!
• 302 Found – Often a temporary redirection to another page, website or resource.
• 304 Not Modified – Means your browser is doing its magic by using a cached copy of the page to speed things up and make life easier for you. You likely will not see this error, but the techies who manage websites or servers can use this to see if their cacheing engines are working.

4xx – Typically Client Errors

These types of errors are often on your side of the playing field. Sometimes it’s user error — you know, when you just type the wrong address in. We’ve all done it, so don’t feel bad.

• 400 Bad Request – This means that the request coming from your web browser is asking for something the web server cannot understand.
• 401 Unauthorized – Up oh! The web page you’re trying to access needs you to say the magic word.
• 403 Forbidden – Sounds scary – because it basically means hands off to the resource your browser is requesting. Often this is because the web developer or host has blocked certain files to protect the site from hackers.
• 404 Not Found – Oh the classic error we see all the time. This simply means that the web address entered doesn’t return anything. As it says, what you’re looking for just isn’t found anywhere on the web server.
• 405 Method Not Allowed – Your browser is trying to communicate with the web server but the method it is trying to use isn’t playing nicely.
• 429 Too Many Requests – Some websites have mechanisms in place that limit how many times in a given timeframe that a request to view the page or site can be made. This helps to prevent denial of service attacks. Just slow it down a bit there partner or try again later.

5xx – Server Errors

When you get an error that is in the 500 range you can almost always chalk it up to something wrong on the server end of things and not on your site of the playing field. These are the types of errors that keep server admin up at night.

• 500 Internal Server Error – There is something stuck in the cogs of the web server’s main engine and it just will not work right. This error means that usually a code error is causing a problem.
• 502 Bad Gateway – The doorway that allows the public to access the website is having a meltdown.
• 503 Service Unavailable – Common with poorly managed shared hosting where the servers are overloaded and just can’t take the pressure. Basically, a server nervous breakdown. These usually are temporary.
• 504 Gateway Timeout – Like the 502 error, this one is all about that doorway taking way too long to open and it basically just responds with, “ain’t gonna happen”.

Whether you are a a regular user visiting a website or a programmer making them, these common codes can help you make sense of things. Some web programmers will create special files that display more user friendly pages other than just a numbered code, but in most cases, knowing the info above can help you make a little sense out of some technical jargon.