> For the complete documentation index, see [llms.txt](https://help.claritylims.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.claritylims.illumina.com/api-and-database/api-docs/rest/http-response-codes-and-errors.md).
# HTTP Response Codes and Errors
The REST API methods attempt to return appropriate HTTP status codes for every request. To use the REST API effectively, a good understanding of HTTP and status codes is required. A complete list of HTTP status codes and definitions can be found at the following website: [HTTP/1.1 Status Code Definitions](http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html)
The primary status codes used by the REST API are as follows:
* **200 OK:** Success.
* **201 Created:** A resource was successfully created.
* **400 Bad Request:** Invalid data was supplied for the relevant resource type.
* **401 Unauthorized:** The requested resource cannot be loaded until valid logon credentials have been entered. If this error is received after logon credentials have been entered, this indicates that the credentials are not valid.
* **403 Forbidden:** Access to the requested resource has been denied. (Make sure that the authorized user has administrative privileges.)
* **404 Not Found:** The URI requested is invalid or the resource requested does not exist.
* **413 Request Entity Too Large:** The request is larger than the server is willing or able to process.
* **500 Internal Server Error:** A generic error message, given when there is no suitable specific message.
### Error message format
Error messages are returned as exception elements with a message element containing a user-facing error message.
The exception may also include a suggested-actions element with more detail on how to resolve the error.
User-facing XML error messages are not returned for 401 and 403 errors. In these cases, the HTTP error must be resolved.
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