What is the difference between index and key-column matching?

Index matching compares row 1 with row 1, row 2 with row 2, and so on — best for ordered exports. Key-column matching pairs rows that share the same value in a chosen column, such as an id, so reordered or inserted rows are matched correctly rather than appearing as a cascade of changes.

How are quoted fields and commas handled?

The parser follows RFC 4180: fields may be wrapped in double quotes, embedded commas inside quotes are preserved, and a doubled quote inside a quoted field is read as a single quote. This handles most spreadsheet exports correctly.

What happens if the two files have different columns?

The tool unions the headers from both files. A column present in only one file shows its cells as added or removed for every row, and the changed-cell highlighting compares matching column names rather than positions.

Why does my whole file show as changed?

With index matching, inserting or deleting a single early row shifts every later row, so each one is compared against the wrong partner. Switch to a key column to pair rows by identity and the noise disappears.

Is my data uploaded anywhere?

No. Parsing and diffing run entirely in your browser in plain JavaScript. No rows are transmitted, so the tool works offline and your data exports stay private.

CSV Diff — Gera Tools

Compare two CSV exports and see exactly which rows were added, removed or changed — matched by row position or by a key column you choose, with the differing cells highlighted. Everything runs in your browser; no file is uploaded.

How it works

Both inputs are parsed with an RFC 4180 reader that handles quoted fields, embedded commas and escaped quotes ("" inside a quoted field becomes a single "). The first row becomes the header.

Then the tool compares rows in one of two modes:

By row index — row n of the left file is compared against row n of the right file. This is correct for ordered exports where rows do not move.
By key column — you pick a column such as id or email; rows are paired by their value in that column. A row whose key exists only on the right is added; only on the left is removed; on both with any differing cell is changed. Reordered or inserted rows are matched correctly.

For each changed row, the tool compares cells by column name (the headers are unioned across both files), so a column present in only one file is shown as added/removed cells.

+ row added     (green)
- row removed    (red)
~ row changed   (amber)  — only the differing cells are highlighted

Tips

Always prefer a key column when comparing database or spreadsheet exports — index matching turns a single inserted row into a wall of false “changes”.
If a key value appears more than once, the tool matches the first unmatched occurrence on each side, then treats remaining duplicates as added/removed.
Trailing blank lines are ignored; surrounding whitespace inside unquoted cells is preserved as-is so you can spot accidental spacing differences.