CSV Diff Checker

A CSV diff checker compares two CSV files and reports which rows were added, which were removed, and which changed, down to the individual cell. Instead of a line-by-line text diff that goes red the moment a single column shifts, it parses both files into rows and columns and compares them as structured data. You paste the old file on the left, the new file on the right, and get four buckets back: added, removed, changed, and unchanged.

The important choice is how rows are paired across the two files. Match by a key column, such as an id or email, and each row is compared to the row that shares its key regardless of where it moved in the file, so re-sorting the export does not create thousands of false changes. Match by position instead, and row one is compared to row one. Key matching is the right mode for database and spreadsheet exports, where the same record can appear on a different line each time you pull the data; positional matching suits fixed-order files like a numbered log.

Everything runs in your browser using an RFC 4180 parser that understands quoted fields, escaped quotes, and commas inside values. The files never leave your device, are never uploaded, and are never logged, which matters because the CSVs people diff are usually customer lists, transaction exports, or inventory tables. Nothing is stored, so the tool keeps working with your network disconnected.

Key-column matching is what makes a CSV diff useful rather than positional, since a row inserted near the top shifts everything below it and a positional comparison reports the whole file as changed. It depends on the key being unique, which is why duplicate keys are flagged rather than silently matched to whichever row came first.

The built-in sample makes a quick check of the CSV diff checker. Both files have the columns id, name, email and plan. With Key: id selected, Compare reports 1 added row (id 5, Erin Park), 1 removed (id 4, Dan Ivanov), 2 changed and 1 unchanged. Expand the changed rows and id 1 shows plan: "pro" -> "team" while id 3 shows only the email cell moving from [email protected] to [email protected]. Bob, on id 2, is counted as unchanged even though nothing about his row is listed.