Gmail to Google Sheets Invoice OCR with OpenAI GPT-4o (n8n)

Turn PDF invoice emails into structured rows in Google Sheets—automatically

This n8n workflow polls your Gmail inbox for PDF invoice/receipt attachments, extracts the text, uses OpenAI GPT-4o to parse key invoice fields into strict JSON, and then appends the results to Google Sheets as a new row—ready for reporting, reconciliation, and downstream automation.

What this workflow does

• Polls Gmail every 15 minutes for messages matching the query: has:attachment filename:pdf (invoice OR receipt).
• Downloads the first PDF attachment found in each matching email and errors if no PDF is present.
• Extracts text from the PDF attachment.
• Sends the extracted text to OpenAI Chat Completions using gpt-4o-mini and requests a strict JSON object containing: vendor, invoice number, dates, currency, and amounts.
• Parses the OpenAI response, adds the sender email address and a processed timestamp, and normalizes missing fields to null.
• Appends a new row to Google Sheets with invoice fields and email metadata.

Use cases

• Accounts payable teams who receive invoices by email and want an always-updated Google Sheets ledger.
• SaaS operators consolidating recurring vendor billing into a single spreadsheet for visibility.
• Automation engineers building invoice ingestion pipelines without manual copy/paste from PDFs.

Technical details

• Gmail Trigger (with a configurable search query and a 15-minute polling interval).
• Extract from file step for PDF text extraction.
• HTTP Request to https://api.openai.com/v1/chat/completions using an OpenAI API credential.
• OpenAI Chat Completions prompt returns strict JSON.
• Google Sheets integration to append rows.

Setup checklist

• Connect Gmail credentials to the Gmail Trigger and ensure you can access the invoice emails mailbox.
• Add OpenAI API credentials for the HTTP request to the Chat Completions endpoint.
• Connect Google Sheets and ensure your sheet has matching columns: Vendor, Invoice #, Date, Due Date, Currency, Subtotal, Tax, Total, Email From, Processed At.