n8n Inventory Reorder Automation: Google Sheets + Gmail + GPT-4 Mini

Auto-reorder inventory from Google Sheets—with Gmail approvals and GPT-4 Mini order confirmation

This n8n workflow audits your inventory and open purchase orders in Google Sheets, calculates what to reorder using measured demand and lead times, and then emails purchase orders to suppliers via Gmail—optionally requesting buyer approval and extracting confirmed quantities from supplier replies with OpenAI (GPT-4 Mini).

What this workflow does

• Runs every weekday morning on a schedule to start a replenishment run and keep your reorder cycle on track.
• Reads multiple Google Sheets tabs (Products, Stockouts, Sales, Purchase orders, Suppliers, and Reorder log) to audit inventory health and purchase order status.
• Flags issues such as late deliveries, short receipts, and stock records that don’t reconcile—then logs follow-up actions back to the Reorder log.
• Chases overdue/short deliveries by emailing suppliers and notifies operations to investigate stock discrepancies (all via Gmail).
• Calculates reorder quantities by measuring demand while excluding stockout days and sales spikes, and determines supplier lead times from receipt history (or falls back to quoted lead time when history is thin).
• Builds one proposed purchase order per supplier, and routes it to: send immediately, hold for a later run, or request buyer approval by email.
• Tracks orders for execution: when an order is sent, it emails the supplier the purchase order and writes each order line into the Purchase orders tab.
• Reconciles supplier responses: polls Gmail for new replies and uses OpenAI (GPT-4 Mini) to extract confirmed quantities/dates/prices from the new reply text only, then updates the order pipeline.

Use cases

• Weekly replenishment runs that reduce stockouts by automatically scheduling reorder emails and logging outcomes.
• Supplier follow-ups for overdue or short deliveries, with an auditable history in Google Sheets.
• Cleaner procurement operations by turning email confirmations into structured updates using GPT-4 Mini.

Technical details

• Google Sheets (Products, Stockouts, Sales, Purchase orders, Suppliers, Reorder log)
• Gmail (supplier chase emails, buyer approval requests, purchase order sending, reply polling)
• OpenAI (GPT-4 Mini) (extracts confirmed quantities/dates/prices from new supplier reply text)
• n8n nodes/stacks: if, set, code, no op, gmail, switch