PDF Invoice Extraction from Gmail to Google Sheets

Overview

This workflow automates the extraction of invoice data from PDF attachments received via email and writes the structured data into Google Sheets. It uses Cradl AI for intelligent document parsing with built-in human-in-the-loop validation, making it ideal for accounting teams that need to process invoices without manual data entry.

How It Works

The workflow is triggered whenever a new email with an invoice PDF arrives in Gmail. It filters only PDF attachments, sends the file to Cradl AI for extraction, splits out individual line items, and appends each line to a Google Sheet. The email is also marked as read to avoid reprocessing.

Node-by-Node Breakdown

1. Gmail Trigger (OAuth2) — Polls Gmail every minute for unread emails matching has:attachment subject:invoice. Downloads all attachments from matching emails. Configured to poll continuously.
2. Filter PDF attachments (No auth required) — A JavaScript code node that iterates over all binary attachments and keeps only those with fileExtension === "pdf". Passes the PDF binary data to the next nodes.
3. Mark a message as read (OAuth2) — Marks the original email as read using the message ID from the trigger, preventing re-processing.
4. Extract invoice details with AI (API Key auth) — Sends the PDF binary to Cradl AI (an AI agent configured to extract invoice fields). The node outputs a JSON object containing invoice-level data and an array of invoice lines.
5. Split out each invoice line (No auth required) — Uses n8n's built-in SplitOut node to split the body.output.invoice_lines array into separate workflow items, one per line item.
6. Add invoice line to Google Sheets (OAuth2) — Appends each invoice line as a new row to a chosen Google Sheets document and sheet. The field mapping is determined by the user when configuring the node.

Setup Instructions

• Gmail: You need a Google account with Gmail enabled. During workflow activation, connect n8n to Gmail via OAuth2 (n8n will guide you through the authorization).
• Cradl AI: Create a free account at Cradl AI and follow the setup to create an invoice extraction agent. Copy your agent ID and API key, then configure the Extract invoice details with AI node with these credentials.
• Google Sheets: Prepare a Google Sheet with columns matching the extracted fields (e.g., Invoice Number, Date, Line Item, Amount, etc.). Authorize n8n to access your Google Drive/Sheets via OAuth2.

Customization

• Email filters: Modify the Gmail Trigger's q parameter to match other senders, subjects, or labels (e.g., from:[email protected]).
• Field mapping: After extraction, you can use an Item Lists node or Code node to transform the Cradl output before writing to Sheets.
• Destination: Swap the Google Sheets node for Xero or QuickBooks nodes (if available) to post invoices directly to accounting software.
• Validation: In your Cradl AI account, you can add human reviewers to approve or correct extracted data before it is exported.

Use Cases and Variations

• Accounts payable automation: Streamline the processing of vendor invoices, reducing manual entry.
• Multi-company mailboxes: Add to:[email protected] to the filter to process invoices sent to a shared inbox.
• Expense reports: Adapt the Cradl agent to extract expense receipt data and write to a budgeting sheet.
• Alerting: Insert a Telegram or Slack node after extraction to notify the team when high-value invoices arrive.

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  "name": "PDF invoice data extraction with human-in-the-loop from GMail to Google Sheets",
  "tags": [],
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      "parameters": {
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        "content": "### How it works\n1. Invoices are imported from GMail  \n2. Data is extracted with Cradl AI  \n3. The extracted data is then written to Google Sheets  \n\n### Setup\n* **Cradl AI action**. Click [here](https://rc.app.cradl.ai/login?redirect=signup&template=n8n%2Finvoices-gmail-to-sheets.json) to create a free Cradl AI account. Choose _n8n_ when prompted for integrations, then follow the setup instructions in the node.  \n* **GMail trigger**. Connect with GMail and customize email filters. For example, if you have a shared mailbox where you receive inboxes you may want to add `to:[email protected]` to the _Search filter_ parameter. \n* **Google Sheets action**. Connect your credentials and map the extracted fields from the Cradl AI output to Google Sheets.  \n\n### Customize\n* The fields that are extracted can be easily customized by logging into your Cradl AI account and updating your agent definition.  \n* Validation rules and reviewers (e.g. from your accounting team) can be added as **human-in-the-loop validators** directly in your Cradl AI account.\n\n### Tutorial\n\n@[youtube](yjVJ8w2U1_M)\n\n"
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        "content": "### Pull invoices from GMail\nThis trigger starts the workflow by getting your invoice file. You can easily swap it with other triggers that fetch files (PDFs or images) from sources like Gmail, webhooks, or cloud storage."
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        "content": "### Export invoice to Google Sheets\nYou can easily swap this out for other destinations, such as accounting tools like Xero or QuickBooks, or a database or data warehouse."
      },
// ... truncated (copy to see full JSON)