A CSV viewer that only lets you read the file is half a tool. The whole reason you opened it is usually that something is wrong — a typo in a header, a stray value in a department column, fifty rows that say "engineering" instead of "Engineering". So the viewer in csvdiff.app now lets you fix all three without leaving the tab.
Like everything else on csvdiff.app, edits stay in your browser. Nothing is uploaded, nothing is logged. Edit a sensitive customer export, download the cleaned CSV, close the tab — done.
Rename Column Headers
Source systems love to give you headers like first_name_v2 or DEPT_CODE_LEGACY. Double-click any header in the viewer and it becomes an inline input — type the new label, press Enter, and the column header updates everywhere it shows up, including in your downloaded CSV. The underlying data keeps its original key, so renames never break a search or a filter you have set up.
- –Double-click the header text to edit
- –Enter or click out to commit; Escape to cancel
- –Renamed labels render verbatim — no forced uppercase
- –CSV export uses the new label as the header row
Edit Individual Cells
Same gesture for the data itself. Double-click any cell, type the corrected value, press Enter. The change is reflected in the search, in row counts, and in the CSV you download. Escape backs out without saving. There is no "Edit mode" toggle to flip — you just click into the cell you want to fix.
Edits are kept in memory for the session. If you reload the tab, you start clean from the original file. We do not write back to your filesystem; the only way edits leave the browser is when you click Download CSV.
Bulk Find & Replace, with a Live Preview
Editing one cell is fine. Editing fifty rows that all say the same wrong thing is exactly the moment a normal viewer hits a wall. Open the column filter on any column, tick the values you want to fix, and a "Replace with…" input appears at the top of the popover. As you type the replacement, a preview block shows every selected value with a strikethrough and an arrow to the new value, plus a count of how many cells will change.
A common case: a department column has "engineering", "Engineering", and "ENG" all referring to the same team. Tick all three values, type "Engineering" into the replace box, and the preview shows you exactly which 47 cells are about to update. Press Enter or click Apply, and the column is normalized in one shot. The filter clears automatically so you can see the cleaned-up table.
- –Multi-select any combination of values to replace
- –Replacement preview updates as you type
- –Per-value counts so you know the blast radius before applying
- –Bulk replace and individual cell edits compose — apply one, then fine-tune the other
Why This Lives in the Diff Tool
Half the time you compare two CSVs, the comparison itself reveals a data-quality issue you need to fix before the merge is useful. Renaming "Dept" to "Department" so two files line up, normalizing case in a status column, correcting a single typo a colleague made — these are the unglamorous-but-frequent jobs around any diff. Now you can do them in the same tab, with the same privacy guarantees, without round-tripping through Excel.
Open a CSV in the viewer, fix what is wrong, download the cleaned file. If you also need to compare it against another version, that is one click away in the diff tool.