Compare two datasets' shape (synth diff)

After changing a generator, or to guard a real feed against drift, synth diff answers whether two files are shaped alike — columns, types, numeric ranges, null rates, category sets — without comparing rows:

synth diff baseline.csv candidate.csv
synth diff baseline.csv candidate.csv --tolerance 0.2 -f json   # for CI

Errors versus warnings

A column added, removed or retyped is an error; a range, null rate or category set that moved past tolerance is a warning. Exit code 1 on any error, 0 on warnings only — the same contract as verify, so a pipeline fails on a structural break and passes on ordinary drift.

The MCP server exposes the same as a diff tool over inline datasets.