How to Compare Two CSV Files

“Did this export change?” is a weekly question in data work. Opening both files in Excel and eyeballing them does not scale past a few hundred rows.

CSVUtility has two different answers, and they are easy to mix up.

1. Saved versus current (unsaved edits)

This is Toggle Diff View. It compares the sheet you are editing with a read-only snapshot of the last saved file.

It is only available when you have unsaved changes (the tool strip enables Diff at that point).

1. Edit the CSV so the file is modified.
2. Click Diff on the tool strip, or Command Palette… (⌘⇧P) → Toggle Diff View.
3. The window title may show Preparing Diff… while CSVUtility reloads the saved baseline from disk.
4. You get two grids that scroll together:

• Left header: Saved · filename (red marker). Cells that exist only on disk, or that changed, tint red.
• Right header: Current / unsaved · filename (green marker). Cells that exist only in the edit, or that changed, tint green.

Both panes are read-only while Diff is on. Clicking the divider without dragging restores equal widths.

Highlights are computed for the cells you can see, so this stays usable on huge files.

Turn Diff off the same way you turned it on.

2. Two different files side by side

That is not Diff View. Right-click a tab and choose Show in Split Screen. You get at most two visible sheets, an adjustable divider, and a complete Find, Sort, Diff, Filter, and Functions strip per pane. Each control talks to the pane that invoked it.

Open the second CSV as its own tab first, then split. Independent filters and finds are the point.

3. Two small files in the browser

If both files are under 15 MB and you are not in the app yet, use the CSV diff tool. It runs in your tab. Nothing is uploaded. Rows line up by position, columns by heading.

Use this for email attachments and vendor samples. Use the Mac app when the files are large, or when the question is “what did I just change in this tab?”

What this diff does not do

CSVUtility’s Diff View is not a Git-style line diff, and it is not a join on an ID column. Cells are compared at the same row and column index after the header. If one side is sorted differently, almost every row will look changed. Sort both the same way first, or compare two exports that share row order.

Delimiter mismatches will also look like a full-file change. Fix format under Settings → Import & Export or by re-opening with the right Import delimiter.

Huge files

Stay in CSVUtility. Both the last save and the live sheet stay on disk as you scroll. Download it here if you are still in a browser.