Invoice checker prompt for ChatGPT, Claude or Gemini

An invoice, yours or one you received. In this prompt version you paste the text yourself. The steps are under "How to use it" below.

Works in ChatGPT, Claude, Gemini or any chatbot. Paste the invoice text or type in its lines and totals. A chatbot without code execution does the sums by hand, so re-add them yourself.

You check an invoice's numbers and completeness. You do not give tax advice: do not say what rate should apply, whether tax is due, or whether a field is legally required.

Invoice (lines, quantities, unit prices, any discount, tax, totals, dates, parties):
[paste]

This invoice is: [one I am sending / one I received]. Currency: [ ]

Do this:
1. Extract each line (description, quantity, unit price, stated line total), any discount, the tax rate and stated tax, the stated subtotal and total.
2. Recompute every line (quantity x unit price), the subtotal, the discount, the tax and the total. If you can run code, use exact decimal arithmetic and say you did. If you cannot, show each sum step by step and say it was done by hand and needs checking. Never state a total from memory.
3. Compare each recomputed number with the stated one. List every difference with both numbers.
4. List which of these common fields are present or absent: supplier name and address, customer name and address, invoice number, invoice date, due date or payment terms, description, quantities and unit prices, currency, payment details, tax or VAT number if tax is shown. Say which are required depends on my country and tax status, which you do not know, so I should check my own rules.
5. Flag: due date before invoice date, dates that do not match the description, mixed currencies, negative quantities, identical lines that may be duplicates, tax applied to a different base than stated, rounding differences of a few pence or cents.

Output: a result line ("all lines and totals match" or "N differences found"), a table of differences (item, stated, recomputed, difference), missing or unclear fields, consistency flags, and questions. Do not correct the invoice silently. Write "not stated" for missing figures. Plain short sentences, no em dashes.

Before: Re-adding an invoice by eye with a calculator, and sending it with the due date before the invoice date.

After (skill output, from a real test run): Test run on a sample invoice we wrote with planted errors. Result, unedited: "2 differences found. Line 2's total is wrong, and that error carries into every total below it." It showed 3 x 18.25 is 54.75 not 55.75, the corrected chain of subtotal, discount, VAT and total, the due date a month before the invoice date, and the missing invoice number, customer address, payment details and VAT number. It changed nothing and said which tax questions to ask an accountant.

• No tax advice. It does not say what rate applies or what a field requires in your country.
• Without code execution it shows the sums by hand and says they need checking.
• It cannot read an image or a scanned PDF. Give it the text or type in the figures.
• It checks arithmetic and completeness, not whether the work was done or the price is fair.

Invoice Checker is also a skill you install once and call in plain words, so you do not paste the prompt each time. It can use its helper scripts and web access where your assistant allows. See the skill page, or read how to install skills.

See every skill for people who run small-business admin.