Paste grid

Paste a CSV or TSV range, tidy it in place, map each column to a SMARTtag field, and see what the import would do — before anything is written.

Or press ⌘V once it is open.

Sample data

Real seeded students, tab-separated — the shape a copied spreadsheet range actually has. One row is a grade change, one has KG (which normalizes), one has an invalid grade, and one student does not exist yet.

Student ID	First Name	Last Name	Grd	Route
207878	Aaron	Herman	5	95
207398	Aaron	Konopelski	KG	
260179	Abel	Grimes	13	195
999412	Marisol	Tavares	4	18B

What to look at

The two-tier header — the source name is editable in place, and the field it maps to sits under it. The grid is the mapping screen; there is no separate wizard step.
First row is a header flips non-destructively — edits and renames survive it in both directions.
A bad cell paints from .field-paint's aria-invalid branch, with no bespoke CSS.
Rejects group by distinct problem, not per row, and cite the line number in your own file.