Extract, validate, and log email invoices from Gmail to Google Sheets with GPT-4

Inbox2Ledger is an end-to-end n8n template that turns a noisy finance inbox into a clean, structured ledger. It fetches emails, uses AI guardrails to keep only finance-relevant messages, extracts invoice/receipt fields via an OCR-style agent, validates and auto-categorizes each expense, generates a unique case ID, and appends the result to a Google Sheet for accounting or downstream automations.

Key Features

• Trigger: Form submission or scheduled fetch (sample On form submission node included)
• AI Filter: Guardrail node determines whether an email is finance-related (payments, invoices, receipts)
• Keyword Filter: Filters common invoice/bill/payment subject keywords
• Extraction: Language-model agent returns normalized JSON:
  • vendor_name
  • invoice_date (YYYY-MM-DD)
  • invoice_id
  • total_amount
  • tax_amount
  • currency
  • items_summary
  • vendor_tax_id
• Validation: Code node checks required fields and amount formats; flags extraction errors
• Categorization: Rule-based expense categorizer (software & hosting, subscriptions, travel, payroll, etc.) with MCC/vendor fallbacks
• Output: Appends structured rows to a Google Sheet with mapped columns:
  • invoice_id, vendor_name, invoice_date, total_amount, currency,
    tax_amount, gl_category, approval_status, timestamp, case_id,
    items_summary, vendor_tax_id, processed_at
• High Accuracy: Low false-positive rate using combined AI guardrails + subject filtering
• Quick Setup: Example nodes and credentials pre-configured in the template

Included Nodes & Flow Highlights

On form submission (date picker trigger)
→ Get Email Content (Gmail)
→ Guardrail: Is Finance? (LangChain Guardrails)
→ IF (Guardrail Passed)
→ Filter Finance Keywords
→ AI Agent (Email OCR)
→ Validate Extraction
→ Check for Errors
→ Apply Finance Rules
→ Log to Invoices Sheet (Google Sheets)

(Full node list and configuration included in the template.)

Requirements & Credentials

• Gmail OAuth2 (read access) — for fetching emails
• OpenAI API key (or compatible LLM) — for guardrails & extraction
• Google Sheets OAuth2 — to append rows to the invoice sheet

Recommended: Use the Google Sheet ID included in the template, or replace it with your own Sheet ID and gid.

Quick Setup Guide

👉 Demo & Setup Video

1. Import the template into n8n
2. Connect and authorize credentials: Gmail, Google Sheets, OpenAI (or preferred LLM)
3. Update the Google Sheet ID / sheet gid if using your own sheet
4. (Optional) Adjust the Guardrail topicalAlignment threshold or filter keywords
5. Test using the form trigger or a single email, then enable the workflow

Configuration Tips

• The extraction agent outputs a strict JSON schema — keep it for reliable downstream mapping
• Use a low LLM temperature (0.2) for deterministic extraction
• For non-USD currencies, ensure your accounting system supports the currency field or add a conversion step
• For high-volume inboxes, enable batching or rate-limit the Gmail node to avoid API quota issues

Privacy & Security

• This template processes real email content and financial data — store credentials securely
• Restrict access to the n8n instance to authorized users only
• Review data-retention policies if using a hosted LLM service

Example Use Cases

• Auto-log vendor invoices from email into an accounting Google Sheet
• Build an audit trail with case IDs for finance teams
• Preprocess incoming receipts before forwarding to AP tools or ERPs

Tags (Recommended)

finance, invoices, email, ai, ocr, google-sheets, automation, accounting, n8n-template