(503) Service Unavailable

The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded. Note that together with this response, a user-friendly page explaining the problem should be sent. This response should be used for temporary conditions and the Retry-After HTTP header should, if possible, contain the estimated time before the recovery of the service. The webmaster must also take care about the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/503

(200) ok
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(201) Created
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(202) Accepted
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(203) Non-Authoritative Information
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(204) No Content
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(205) Reset Content
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(206) Partial Content
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(300) Multiple Choices
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(301) Moved Permanently
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(302) Found
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(304) Not Modified
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(307) Temporary Redirect
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(308) Permanent Redirect
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(400) Bad Request
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(401) Unauthorized
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(402) Payment Required
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(403) Forbidden
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(404) Not Found
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(405) Method Not Allowed
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(406) Not Acceptable
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(407) Proxy Authentication Required
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(408) Request Timeout
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(409) Conflict
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(410) Gone
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(411) Length Required
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(412) Precondition Failed
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(413) Payload Too Large
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(414) URI Too Long
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(415) Unsupported Media Type
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(416) Range Not Satisfiable
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(417) Expectation Failed
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(422) Unprocessable Entity
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(425) Too Early
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(426) Upgrade Required
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(428) Precondition Required
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(429) Too Many Requests
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(431) Request Header Fields Too Large
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(451) 451 Unavailable For Legal Reasons
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(500) Internal Server Error
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(501) Not Implemented
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(502) Bad Gateway
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(503) Service Unavailable
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(504) Gateway Timeout
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(505) HTTP Version Not Supported
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(506) Variant Also Negotiates
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(507) Insufficient Storage
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(508) Loop Detected
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(510) Not Extended
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(511) Network Authentication Required
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