input-validation

# 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.