Gmail Receipt OCR to Google Sheets with Gemini & Slack Alerts (n8n)

Automatically turn Gmail receipt attachments into Google Sheets expense rows—complete with Gemini extraction and Slack alerts

This n8n workflow watches your inbox for receipt/invoice emails, extracts expense details using Google Gemini, logs everything into Google Sheets, and notifies Finance in Slack when an expense crosses your configured limit—then sends confirmation emails to employees.

What this workflow does

• Monitors Gmail every minute for incoming receipt/invoice/expense messages with attachments, downloads the attachment, and proceeds when a match is found.
• Uses Gemini Receipt OCR extraction: sends the attachment image to Google Gemini to extract structured fields (e.g., vendor, date, amount, tax, currency, category, payment method, and more) as JSON.
• Parses, validates, and enriches the AI JSON, adds the Gmail sender as the employee fallback, generates an expense ID, and flags whether the amount exceeds the configured expense limit.
• Writes to Google Sheets: appends or updates the expense record using the Expense ID as the matching key.
• Triggers Slack + email workflows:
  • If the expense is over the limit, posts an approval-required alert in a Slack finance channel, then emails the employee a processed receipt notification.
  • If it’s within the limit, emails the employee a processed receipt notification.
• Generates a monthly report: runs on a schedule, reads all rows from Google Sheets, calculates totals (amount, tax, averages, category and employee breakdowns, and highest expense), and emails the monthly report to Finance via Gmail.

Use cases

• Expense reimbursement workflows where receipts arrive via Gmail with attachments
• Small finance teams needing Slack approvals for out-of-policy spending
• Automation engineers deploying reliable Gmail → Gemini → Google Sheets data pipelines in n8n

Technical details

• n8n trigger: Gmail receipt/invoice query polling (every minute)
• Integrations: Gmail (trigger + send), Google Sheets, Slack, Google Gemini
• Workflow logic: if, code, and other supporting nodes (e.g., receipt handling and notes)
• AI output handling: JSON extraction, parsing/validation, and expense limit flagging