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The HTTP Status Codes You Need to Know

markmichon profile image Mark Michon Originally published at blog.bearer.sh ・1 min read

Working on the web means coming into contact with HTTP responses. Whether you spend your time primarily on the client or on the server, you're likely familiar with the popular ones like 200, 404, and 500. While memorizing all the codes using cat memes as a mnemonic can be helpful, let's dive deeper into what some of the most common codes mean.

What is an HTTP status code?

HTTP response status codes are a set of standardized and agreed upon numbers that identify information about an http response.

Status codes are 3 digits and broken down into 5 categories, each organized by the first digit of the number. You'll see these abbreviated as the first number, followed by two "x" characters. For example, "4xx".

  • 1xx: Informational provides information about a request in progress.
  • 2xx: Successful indicates that the request was received and accepted.
  • 3xx: Redirection indicates that the request has to be redirected.
  • 4xx: Client Error indicates that an error has occurred on the client.
  • 5xx: Server Error indicates that an error has occurred on the server.

If you're consuming an API, it is usually safe to assume that it conforms to these standardized codes. If you are the one creating an API, make sure to match your responses with the appropriate code.

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citizen428 profile image
Michael Kohl

Someone on Twitter once summarized it along these lines and I've been using this to teach status codes for a while now:

1xx: I thought you should know
2xx: All good
3xx: Look somewhere else
4xx: You messed up
5xx: We messed up

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murkrage profile image
Mike Ekkel

This is a great way of remembering it! Makes total sense as well.

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george profile image
George Nance

Great article, but I think you forgot to mention a very important http code : 418

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markmichon profile image
Mark Michon Author

It was certainly in an early draft 😅

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reritom profile image
Tomas Sheers

I use the Mozilla http status thing developer.mozilla.org/en-US/docs/W...

But I'm wondering, if the client sends a request to a RESTful api to create something like a resource allocation, where the request and references are valid, but the allocation already exists and so therefore another can't be made, what status code would be best to reflect that?

The 406 title seems correct for this, but the description seems to technical.

409 could work if you consider conflict as a functional conflict.

I don't seem to find a good HTTP code to reflect that the payload and request was valid, but the resource couldn't be created for functional reasons.

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xanderyzwich profile image
Corey McCarty

I'd typically consider such a thing as 200 with a response that includes some sort of error/exception code/explanation. The thing already exists, but the request was received, processed, and responded to appropriately. This should be a part of your contract design for the API itself. I personally believe that something that is data related shouldn't return http code other than success. Perhaps adoption of 201 as successful creation/allocation and 200 as non-error without creation having occurred.

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reritom profile image
Tomas Sheers

I haven't considered using 200 before for valid requests that can't be processed. But it does make sense. I've typically used: 200 OK (for getting valid resources, and for resource deletions), 201 for resource creation, 404 for invalid resource ids or missing routes, and from there I just imagined that a 4XX code would be used to indicate that the request was functionally invalid.

This was based on seeing some consumers of APIs where in python they would do "response = requests.get(...)" and then check if the response is "ok" by using "if response.ok: ...". So that in that case 2XX is ok, and anything else is not ok, so one would expect the failed resource to be in the "not ok", so not a 2XX. But this was just extrapolation. Maybe it is better for all valid requests to be 2XX, but would require more client side logic.

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Mark Michon Author

When creating a resource, ideally you'd have some mechanism in place to dynamically generate the unique references(ID, etc).

If, however, you're creating user accounts bound to a user id or email, you may run into a scenario like the one you've mentioned. In that case, the 409 seems more appropriate if you want to avoid the generic 400. I wouldn't use 406.

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reritom profile image
Tomas Sheers

This is what I would expect, but Coreys reply makes sense too. I wonder if there is some specification for this, or what the general consensus is.

I've worked with a few REST APIs and most haven't been consistent in this regard.

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kulpras profile image