Reject bad requests at the edge before they touch real logic or a database A 40-line validator with zero dependencies handles most of my needs Check shape, types, and size limits first, then business rules later Returning 400 early cut wasted function runs on one endpoint by half Most of the junk that hits an API never deserved a full response. A malformed body, a missing field, a 4MB payload where I expected 2KB. I catch all of that at the edge now, before a single line of rea...