CSV Compare & Reconcile Skill

Two exports that should match but don't: last month's and this month's price list, yesterday's and today's inventory, invoices and payments. This tool answers two questions in one command:

• What changed? It matches rows by a key (SKU, email, ID; detected automatically) and lists added, removed and changed rows, cell by cell, with the change in amount and percent.
• Why don't the totals match? It sums an amount per key in each file and lists amounts that differ and keys found in only one file. A check line shows the differences add up to the total gap.

It runs on your computer with Python 3.9+ and no installs, and it's a Claude Code skill (skills/csv-compare/).

$ python3 -m csvcompare examples/products-2026-10.csv examples/products-2026-11.csv --out compare/
- Rows: 35 -> 37
- Key: SKU (detected)
- Added: 3, removed: 2, changed: 11 rows (11 cells)
- Same value, different format (not counted): 3 cells
- Columns only in new file: Supplier
- Repeated keys (only the first row is compared): old none; new HK-1011
- Leading zeros lost in 2 cells (often a file saved from Excel): HK-1018 Barcode 049028987155->49028987155, ...
| HK-1003 | Price | 24.00 | 27.00 | +3.00 (+12.5%) |

$ python3 -m csvcompare reconcile examples/invoices.csv examples/payments.csv --key invoice_number --key-b Invoice --amount amount --amount-b Amount --ignore-case
- Totals: 32,910.00 vs 32,775.00 (difference -135.00)
- Matched: 26, amount differs: 2, only in A: 2, only in B: 1
| INV-2026-0027 | 1,200.00 | 2,400.00 | +1,200.00 | 1/2 |      <- paid twice
| INV-2026-0015 | 780.00 | 755.00 | -25.00 | 1/1 |              <- short paid
Check: mismatches +1,175.00, only in A -1,950.00, only in B +640.00 = -135.00 (total difference -135.00)

• Columns in a different order or with different capitalization; columns found in only one file are listed.
• Values that differ only in format count as the same: 1,299.00 vs 1299, $1,200.00 vs 1200, 2026-11-09 vs 11/09/2026, extra spaces. Use --exact to turn this off, --tolerance 0.01 for rounding and --dayfirst for dd/mm dates.
• Leading zeros lost (zip codes, barcodes, employee IDs after a trip through Excel) are reported separately instead of as changes.
• Repeated keys, rows with an empty key or an unreadable amount, split payments (several rows per key in reconcile), and comma, semicolon, tab or pipe files in UTF-8, UTF-16 or Windows-1252.
• No key column? Whole rows are compared, and the report says to pass --key.

Exit code 0 when the files match, 1 when there are differences, 2 on an error. So it works in scripts and scheduled checks.

Save each sheet as CSV (File > Save As > CSV UTF-8) and compare the CSVs.

./demo.sh runs both modes on the examples. ./run_tests.sh runs the tests.

The tool does arithmetic on the files you give it. It isn't accounting advice, and a person decides what to do about each difference.

Related: CSV Data Quality Checker (free) cleans each file first: https://youraitools.co/marketplace/csv-data-quality-checker. Bank Reconciliation Exceptions Skill covers bank statements against the ledger: https://youraitools.co/marketplace/bank-reconciliation-exceptions-skill

• Save each Excel sheet as CSV (File > Save As > CSV UTF-8) and compare the CSVs.
• The tool does arithmetic on the files you give it.
• It isn't accounting advice, and a person decides what to do about each difference.