Built N8N Validator That Caught Vendor's 50-Cent Math Error 🔥

Duy Bui

🔥

10h (edited) • General Discussion 💬

Friend runs manufacturing shop. Processes 40 purchase orders monthly.

Last month approved one where vendor miscalculated the line item total.

Line item said: 47 units at $23.50 each equals $1,105.00

Real math: 47 × $23.50 = $1,104.50

Fifty cent error. Small right?

Multiply that across multiple vendors over months? His exact words: "Holy shit, this adds up."

THE N8N WORKFLOW

Built 9-node workflow watching his procurement inbox automatically.

Gmail trigger fires when new PO email arrives → Downloads attachment file → Extracts structured data → Validates all calculations → Checks budget threshold → Logs to Google Sheets → Routes to Slack appropriately

Over $10K budget? Sends approval request with full financial breakdown to manager

Under $10K budget? Auto-approves with confirmation notification to team

Math doesn't check out? Rejects immediately with specific errors listed

WHAT IT VALIDATES

Line item math checking: quantity times unit price equals listed total amount?

Subtotal accuracy verification: sum of all line item totals matches subtotal?

Final total calculation: subtotal plus tax equals final total on PO?

Budget compliance check: total amount under threshold limit?

Date logic validation: delivery date comes after order date?

System flags anything wrong immediately with specific error details.

THE PROCESSING RESULTS

Processing 40 POs monthly now. Takes 30 seconds automated validation versus 15 minutes manual checking before.

Four month statistics tracked:

160 POs validated automatically without human intervention

11 math errors caught before approval went through

48 over-budget items flagged correctly for manager approval

Zero calculation errors reached accounting department

Complete audit trail maintained in Google Sheets

Google Sheets database tracks everything comprehensively. PO details with vendor information. Complete line items breakdown. Validation results with pass/fail status. Submitter identification. Processing timestamp for audits.

Slack notifications keep entire team informed real-time. Approval requests show full context with budget comparison. Auto-approvals confirm within-budget status clearly. Everyone knows PO status immediately.

Friend's reaction: "This thing is legitimately better at math than I am. Never misses anything."

Saves him 10 hours monthly from manual checking. Catches calculation errors he would miss scanning quickly. Enforces budget rules consistently without forgetting threshold.

The workflow JSON available here . Import to n8n instance. Connect Gmail account for procurement inbox. Connect Google Sheets for tracking. Connect Slack workspace for notifications. Customize budget threshold amount. Test with sample POs. Deploy to production.

Setup takes 20 minutes total. Runs continuously after deployment. Minimal maintenance required.

What manual checking errors are you catching too late?

8 comments