sheetdelta

Compare two Excel workbooks and find out what actually changed.

sheetdelta reads two .xlsx files, shows you the difference cell by cell, and then tells you which of those changes reach other cells. It runs on Linux, in CI, with no copy of Excel anywhere near it.

$ sheetdelta diff budget_v1.xlsx budget_v2.xlsx
budget_v1.xlsx  ->  budget_v2.xlsx

Sheet 'Revenue'  (1 change, 1 breaking)
  !! D12    formula changed
          -  =SUM(D2:D11)
          +  =SUM(D2:D13)
        affects 3 cells downstream: Revenue!E12, Revenue!F12, Summary!B4

Sheet 'Summary'  (1 change)
  !  B7     value changed
          -  1200
          +  1450

1 formula; 1 value across 2 edited sheet(s). 1 breaking change reaching 3 downstream cells.

Why

Two things go wrong when a spreadsheet changes and nobody looks closely.

The first is the change itself. git diff on an .xlsx gives you binary noise, so the usual answer is to open both files side by side and squint.

The second is worse. A formula edit looks harmless on the sheet you are looking at, but the cell feeds a summary three sheets away. The number that matters is now wrong, and nothing tells you.

sheetdelta answers both. Every change is followed through the dependency graph, so a formula edit reports the cells it reaches, and a CI job can fail the build on exactly that.

Install

pip install sheetdelta

No dependencies. The reader is zipfile and xml.etree from the standard library, so it drops into any environment, including a build container that has nothing but Python.

Usage

Compare two workbooks

sheetdelta diff old.xlsx new.xlsx

Exit status is 0 when nothing breaking changed, 1 when something did, 2 on an error. That makes it a CI check without any extra scripting:

- run: pip install sheetdelta
- run: sheetdelta diff before.xlsx after.xlsx --fail-on breaking

--fail-on takes three values:

Machine-readable output

sheetdelta diff old.xlsx new.xlsx --json

{
  "old": "budget_v1.xlsx",
  "new": "budget_v2.xlsx",
  "has_changes": true,
  "summary": {
    "cell_changes": {"formula": 1, "value": 1},
    "breaking": 1
  },
  "sheets": [
    {
      "kind": "changed",
      "name": "Revenue",
      "old_name": "Revenue",
      "changes": [
        {
          "cell": "Revenue!D12",
          "a1": "D12",
          "kind": "formula",
          "severity": "breaking",
          "detail": "formula changed",
          "old": "=SUM(D2:D11)",
          "new": "=SUM(D2:D13)",
          "affected": ["Revenue!E12", "Revenue!F12", "Summary!B4"]
        }
      ]
    }
  ]
}

Check one workbook

sheetdelta audit workbook.xlsx

An audit looks for the two defects that make a workbook unsound:

• a formula pointing at a sheet that does not exist, which Excel turns into #REF! when it recalculates; and
• a circular reference, a cell that depends on itself through a chain of other cells, which Excel refuses to calculate at all.

$ sheetdelta audit model.xlsx
model.xlsx
  3 sheet(s), 412 cell(s), 118 formula(s)

1 broken reference(s):
  !! C4     Removed Sheet!B2
        sheet 'Removed Sheet' does not exist
        ='Removed Sheet'!B2*1.2

1 circular reference(s):
  !! Revenue!D12 -> Revenue!E12 -> Summary!B4 -> Revenue!D12

A reference to a cell that is simply empty is not reported. That is normal in a spreadsheet, and flagging it would make the audit useless on real files.

What it reports

The stale case is worth explaining. Excel stores both a formula and the last value it calculated for it. When a file is edited by something that does not recalculate, the two disagree. Excel will happily show you the new formula next to the old number, which is a quiet way to ship a wrong total. sheetdelta flags it.

A rename is detected by matching the contents of a removed sheet against an added one. Without that, renaming a sheet would look like every cell in it changed and bury the real diff.

What it does not do

Being clear about this saves you time.

• It does not evaluate formulas. There is no calculation engine, and there will not be one. Excel already stored the value it last computed, and that is what gets compared. This is why the tool needs no Excel and no dependencies, and why it is fast on large files.
• It does not write or edit workbooks. Read-only, by design.
• It only reads .xlsx and .xlsm. The old .xls and binary .xlsb formats are rejected with a clear message rather than half-parsed.
• It does not align rows across an insertion. If a row is inserted near the top, every cell below it reports as changed. Matching rows by content is the hard part of spreadsheet diffing and is not implemented yet.
• It does not read VBA macros inside .xlsm files.

Using it as a library

from sheetdelta import diff_workbooks, read_workbook

result = diff_workbooks(read_workbook("old.xlsx"), read_workbook("new.xlsx"))

for change in result.breaking:
    print(change.ref, "->", change.affected)
    print("  was", change.old)
    print("  now", change.new)

Every type is exported from the package root, and the whole thing is typed.

How it works

An .xlsx file is a zip containing XML. sheetdelta reads the sheet list, the shared string table, the number formats and each sheet's cells, then stops.

Each formula is scanned for the cells and ranges it mentions. That scan is more careful than it looks: LOG10(...) looks exactly like a reference to column LOG row 10, and "see A1" looks like a reference to A1. Both are handled, because a dependency graph built on false references is worse than no graph.

References are kept as ranges rather than expanded. SUM(A:A) covers a million cells, and expanding it would cost more than the entire diff; the graph asks whether a range contains a cell instead.

Requirements

Python 3.10 or newer. No runtime dependencies.

License

MIT.