Understanding HTTP’s status codes

Following our series on HTTP, here is a quick note on HTTP status code, sent with the HTTP response. They are organized in 5 categories:

1xx Informational, ex:

• 100 Continue used when doing a multi-part file upload
• 101 Switching Protocol used when switching from HTTP to WebSocket

2xx Success, ex:

• 200 OK all is good the client received the resource
• 201 Created used mostly with REST API to mean the resource has been created

3xx Redirection, ex:

• 301 Moved Permanently the redirect to use for SEO so that Google follow/index the link
• 304 Not Modified meaning the client can use its local cached copy

4xx Client Error, ex:

• 400 Bad Request the generic bad request response
• 413 Payload Too Large often means the file uploaded is too big

5xx Server Error, ex:

• 502 Bad Gateway often means your application server is down
• 504 Gateway Timeout often means the web/application server took too long to reply

For a simple and exhaustive list, checkout httpstatuses.com. All codes are there with an explanation and code references in various programming languages.