# n8n Invoice Processing Automation
Production-ready n8n workflow for automated invoice ingestion, classification, extraction, normalization, and logging using Google Drive, LLMs, and Google Sheets.
## Overview
## Workflow Overview
This workflow automatically processes invoices uploaded to a Google Drive folder.
It supports **native PDFs** and **scanned PDFs/images**, applies the correct extraction strategy, normalizes the data, validates results, and logs outcomes.
Designed with:
- Clear branching logic
- Deterministic parsing
- Defensive normalization
- Audit-friendly outputs
## Workflow Architecture
1. **Google Drive Trigger**
- Watches a specific folder for new files
2. **File Download**
- Retrieves the uploaded document
3. **PDF vs Image Detection**
- Identifies whether the file is a PDF or image
4. **Native vs Scanned PDF Detection**
- Uses text density heuristics to classify PDFs
5. **Data Extraction**
- Native PDFs → Text extraction + OpenAI
- Scanned PDFs / Images → Vision model (Gemini)
6. **LLM Output Parsing**
- Strict JSON extraction
- Model-agnostic defensive parsing
7. **Normalization & Validation**
- Date normalization (multiple formats)
- Currency normalization
- Numeric coercion
- Validation contract (is\_valid)
8. **Google Sheets Logging**
- Clean invoices → main sheet
- Invalid invoices → error sheet (optional extension)
## Extracted Fields
- Date
- Invoice Number
- Vendor
- Tax ID
- Subtotal
- Tax
- Total
- Currency
- Description
All fields are **null-safe**. No inference or guessing.
## Key Design Decisions
- No brittle regex-based extraction
- LLMs constrained to strict JSON output
- Explicit normalization layer
- Separation between extraction, parsing, and validation
- Credential-free export for safe sharing
## Requirements
- n8n v2+
- Google Drive credentials
- Google Sheets credentials
- OpenAI API key
- (Optional) Google Gemini API key for image invoices
## Setup Instructions
1. Import the JSON workflow into n8n
2. Create credentials for:
- Google Drive
- Google Sheets
- OpenAI
- Gemini (optional)
3. Replace placeholder IDs:
- Google Drive folder ID
- Google Sheets document ID
4. Activate the workflow
5. Upload an invoice to the watched folder
## Use Cases
- Accounting automation
- Expense tracking
- Invoice digitization
- Finance ops workflows
- AI-assisted document processing
## Notes
This repository intentionally excludes credentials and cached metadata.
All sensitive values must be configured manually after import.
**Author:**
Automation & AI Workflow Engineer
Specialized in n8n, LLM pipelines, and document automation