Income and expense log from Gmail invoices and receipts

Income and expense log from Gmail invoices and receipts

An n8n workflow for small-business bookkeeping. It watches your Gmail inbox, and when an email arrives with a file attached,
it saves the first attachment to Google Drive and has Mistral AI read the text out of it. GPT-4.1 mini then decides whether the
email is about money at all, and if so, whether the money came in or went out. An agent pulls out the date, amount, currency and
reference, and the workflow adds a row to a Transactions tab in Google Sheets, with a link to the file in Drive.

What is inside

• workflow.json: the workflow as n8n exports it, nineteen nodes with no sticky notes. It holds no credential.
• README.md: these notes.

What we changed from the original copy

• The author's spreadsheet is gone. Read Chart of Accounts, Add Expense to Transactions Sheet and
  Add Income to Transactions Sheet ask for YOUR_SHEET_ID and find their tabs by name: Chart of Accounts and
  Transactions.
• The income or expense rules in Check if it’s revenue or expense named a company as "my company". That name now reads
  YOUR_COMPANY_NAME, so the model knows which invoices you send and which you receive.
• Nothing else changed. The original copy needed no backslash repair.

Before you start

• An n8n instance, on n8n Cloud or your own server.
• A Gmail account that receives your invoices and receipts.
• A Google account with Google Drive and Google Sheets (the same account works).
• An OpenAI API key that can use gpt-4.1-mini.
• A Mistral AI API key, for reading the attachments.

Set it up

1. In n8n, create a workflow, open its menu and choose Import from File. Pick workflow.json.
2. Add a Gmail OAuth2 credential and select it in Gmail Trigger.
3. Add a Google Drive OAuth2 credential and select it in Upload file and Download file.
4. Make the spreadsheet (below) and copy its ID, the long part of its address between /d/ and /edit. Add a Google Sheets
   OAuth2 credential and select it in the three sheet nodes, then replace YOUR_SHEET_ID in each with the ID.
5. Add an OpenAI credential and select it in OpenAI Chat Model, OpenAI Chat Model1, OpenAI Chat Model2 and
   OpenAI Chat Model3.
6. Add a Mistral Cloud credential with your Mistral AI key and select it in Extract text.
7. Open Check if it’s revenue or expense, find rule 5 in its system prompt and replace YOUR_COMPANY_NAME with your
   business's name.
8. Read Good to know before you publish. Emails without an attachment stop with an error as the file comes, and the fix is
   given there.
9. Save, send yourself an invoice with a PDF attached, run the workflow once from the editor, then press Publish.

The spreadsheet

One Google Sheet with two tabs:

• Chart of Accounts: your categories, one a row, with whatever columns you keep (a name, and income or expense, for
  example). Every row is handed to the models as context.
• Transactions: the headers TransactionID, Date, Type, Category, Invoice Link, Amount and Description.
  The amount header ends with a space in the file. Type it the same way, or rename the column in both Add nodes.

How a run goes

1. Gmail Trigger checks the inbox every minute and fetches each new email in full, with its attachments.
2. If Email Contains Document sends emails with an attachment one way and the rest another.
3. With an attachment: Upload file saves the first one to the root of your Drive, Download file fetches it back, and
   Extract text sends it to Mistral's OCR model, which returns its text.
4. Check for Transaction Email reads the extracted text, the subject, the body and the sender. GPT-4.1 mini sorts the email
   as a transaction or not. Anything else stops here.
5. Read Chart of Accounts and Aggregate Categories turn the categories tab into one list.
6. Check if it’s revenue or expense sorts the transaction as Expense or Income, using the rules and examples in its prompt.
7. Expense AI Agent or Income AI Agent pulls out the transaction ID, the date as DD/MM/YYYY, the type, the amount, the
   currency symbol and a comment, as JSON.
8. Add Expense to Transactions Sheet or Add Income to Transactions Sheet appends a row: the type goes in Category, the
   comment in Description, the currency and amount together in Amount , and the Drive link in Invoice Link.

Change the look

• What counts as a transaction: the two categories and their descriptions in Check for Transaction Email.
• Income or expense: the rules and examples in the system prompt of Check if it’s revenue or expense.
• What it records: the field list in each agent's system message and the example in each Structured Output Parser. Add a
  field in both, then map it in the matching Add node.
• How often it checks: Poll Times in Gmail Trigger.

Good to know

• Emails without an attachment fail: that path skips Extract text and Upload file, but the later nodes still read
  $('Extract text').item and $('Upload file').item. n8n stops such a run with "Node 'Extract text' hasn't been executed".
  To fix it, wrap each of those reads in isExecuted, for example
  {{ $('Extract text').isExecuted ? $('Extract text').item.json.extractedText : '' }}. They sit in
  Check if it’s revenue or expense, both agents' prompts and the Invoice Link of both Add nodes.
• The category: the chart of accounts goes to the models, but nothing asks them to pick from it. Category gets the type
  the agent describes, such as "Subscription Renewal". To get your own names, tell both agents to choose from the chart.
• Every attachment is saved: the upload happens before the email is checked, so newsletters and tickets land in your Drive too.
  Each file is named attachment_0, since that is the fixed name in Upload file. Only the first attachment of an email is read.
• Amounts are text: an expense is written as a minus sign, the symbol and the number (-₹140.00), and income as the symbol
  and the number. Sheets may keep them as text, so sums need a helper column.
• Billing: every new email costs at least one GPT-4.1 mini call, and a transaction up to three. Mistral bills each attachment
  it reads, whether or not it turns out to be a transaction.
• GPT-4.1 mini: OpenAI's deprecations page, read on 2 November 2026, removes gpt-4.1-mini-2025-04-14, the model behind
  gpt-4.1-mini, on 14 January 2027 and recommends gpt-6-luna. Change the four chat model nodes before then.
• Both agents' system messages begin with a stray =. The models ignore it.
• Duplicates: nothing checks the sheet first, so an email that arrives twice is logged twice.
• Your data: the emails' text and their attachments go to OpenAI and Mistral, and the attachments stay in your Drive. Check
  each row against its file before your books rely on it, since a model can misread a figure or a date.