One bad VLOOKUP can cost days. SheetSage scans for 5 critical errors: risky VLOOKUPs returning wrong data, out-of-bounds lookups, unsafe MATCH functions, drifting ranges that break when copied, and hidden magic numbers. Groups thousands of similar errors into fixable cards. One-click bulk fixes with auto-backup. Health Score at a glance. Runs locally—zero uploads. For finance teams and anyone who's questioned a spreadsheet number at midnight.