What Are 4xx Client Error Responses?
HTTP 4xx Client Error Responses indicate that the request sent by the client cannot be completed.
The problem is usually caused by invalid input, missing authentication, or insufficient permissions.
Common 4xx Status Codes
400 Bad Request - The request contains invalid data.
401 Unauthorized - Authentication is required.
403 Forbidden - Access is denied.
404 Not Found - The resource does not exist.
400 Bad Request
A 400 response means the server cannot understand the request.
401 Unauthorized
A 401 response indicates that authentication is missing or invalid.
403 Forbidden
A 403 response means the user is authenticated but does not have permission to access the resource.
404 Not Found
A 404 response means the requested resource does not exist.
Why 4xx Responses Matter For DevOps
Debugging APIs
Monitoring application behaviour
Finding broken routes
Improving security controls
Summary
HTTP 4xx responses help engineers identify problems caused by client requests and user interaction.