Free · no account
Drag a cell down in Excel or Sheets and it quietly increments the number. The code still looks like a code. Nothing tells you otherwise until a society or a store rejects it — often months later, after the sheet has been copied twice.
ISWCs and barcodes carry a check digit, so for those the arithmetic settles it. An ISRC carries none — there we can prove the shape is right and catch the same code used on two tracks, which is most of what a spreadsheet gets wrong. Paste your list.