Input Validation

Validate at the edge, before the data touches logic or storage.

• Schema — type, required fields, allowed values. Reject unknown fields rather than ignoring them.
• Bounds — string length, number ranges, array size. An unbounded input is a DoS and a memory bomb.
• Format — emails, UUIDs, dates parsed and re-validated, not trusted as strings.
• Files — size limit, type allowlist (check content, not just extension), no path traversal in names.
• Reject with a clear 4xx and a message that says what's wrong — without leaking internals.

Never trust "it comes from our own frontend". The request can come from anywhere.