HTTP Common Errors and Debugging

curl -s -o /dev/null -w '%{http_code}
' https://example.com/health

# Useful for scripts and health checks.

curl -s -o /dev/null -D - https://example.com | grep -i '^location:'

# Show the redirect location without fully following it.

curl -s -o /dev/null -w 'code=%{http_code} time=%{time_total}
' https://example.com

# Inspect total time and status code together.

curl -i -X POST https://example.com/api/users -H 'Content-Type: application/json' -d '{"name":"Ada"}'

# Test common API validation and auth failures.

401 = not authenticated / invalid credentials
403 = authenticated but forbidden

# Authentication versus authorization.

404 = not found
410 = gone permanently

# Missing resource versus intentionally removed resource.

301 = permanent
302 = temporary
307 = temporary, preserve method
308 = permanent, preserve method

# Choose the right redirect semantics.

502 = bad upstream response
503 = service unavailable / overloaded / maintenance
504 = upstream timeout

# Gateway and availability failures.

304 Not Modified
412 Precondition Failed

# Conditional request and cache-related statuses.