Your Database MCP Is Lying to You

A Postgres MCP agent misread a jsonb field and reported zero express-delivery orders because it queried the wrong key.

The empty result looked legitimate, showing how schema inference errors can hide inside apparently valid SQL output.

Row sampling alone is not enough; in-database recursive CTEs and functions like jsonb_each, jsonb_array_elements, and jsonb_typeof can reveal the real JSON structure.

Server-side traversal and aggregation make semi-structured data safer for agents by reducing confident but wrong claims.