Exploring 4xx HTTP Status Codes: Causes, Examples, and Fixes

 Common 400 HTTP Status Codes and Causes

Here’s a detailed explanation of common 4xx HTTP status codes, which indicate client-side errors—meaning the request sent to the server was incorrect or cannot be fulfilled.

Common 4xx Status Codes

400 Bad Request

• Meaning: The server cannot process the request due to malformed syntax.
• Causes:
• Invalid URL or query parameters
• Corrupted request payload
• Missing required headers
• Example: Sending a JSON payload with incorrect formatting.

401 Unauthorized

• Meaning: Authentication is required and has either failed or not been provided.
• Causes:
• Missing or invalid API key/token
• Incorrect login credentials
• Note: Often used with WWW-Authenticate header to indicate how to authenticate.
• Example: Accessing a protected resource without logging in.

403 Forbidden

• Meaning: The server understands the request but refuses to authorize it.
• Causes:
• Insufficient permissions
• IP or user blocked
• Access control rules denying access
• Example: Attempting to access an admin page without the necessary admin rights.

404 Not Found

• Meaning: The requested resource could not be found on the server.
• Causes:
• Incorrect URL
• Deleted or moved resource
• Example: Visiting a broken link or a URL with a typo.

405 Method Not Allowed

• Meaning: The HTTP method used is not allowed for the requested resource.
• Causes:
• Using POST on a resource that only accepts GET
• Example: Trying to delete a resource using GET instead of DELETE.

408 Request Timeout

• Meaning: The server timed out waiting for the client to send the full request.
• Causes:
• Slow internet connection
• The client took too long to send data
• Example: A form submission that stalls before completion.

409 Conflict

• Meaning: The request could not be completed due to a conflict with the current state of the resource.
• Causes:
• Duplicate entries
• Versioning conflicts in APIs
• Example: Trying to create a user with an email that already exists.

410 Gone

• Meaning: The resource is no longer available and will not be available again.
• Causes:
• Resource intentionally removed
• Deprecated API endpoint
• Example: Accessing a page that has been permanently deleted.

429 Too Many Requests

• Meaning: The user has sent too many requests in a given time (rate limiting).
• Causes:
• API abuse
• Bot traffic
• Example: Making hundreds of API calls in a few seconds.