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2026

WhatsApp assistant on the Meta Cloud API

Node.js
Express
PostgreSQL
Docker
WhatsApp Cloud API
Claude API

Description

An assistant that answers a business's WhatsApp and books the appointment during the conversation. It runs on Meta's official Cloud API, approved through their app review, and reaches my scheduling platform through three tools and nothing else.

Features

  • Runs on Meta's official Cloud API, approved through Meta's app review
  • Three tools and none of them destructive: list services, list openings, book
  • Coexistence by QR code, so the owner keeps using WhatsApp on her own phone
  • Reads the existing appointments before every reply, instead of trusting the conversation
  • Rate limiting per phone number rather than per IP address

Challenges

  • Getting through Meta's app review, which asks for a verified business and a real use case rather than a demo
  • Keeping the model from booking a slot that was already taken, which meant reading the agenda before every message
  • Limiting abuse when every request reaches the API from the same server address

Learnings

  • That a model cannot delete what it has no tool for, and that is a stronger guarantee than an instruction written in the prompt
  • That coexistence with the phone, not the API itself, is what decides whether a small business accepts the thing
  • How much of an integration's cost is the provider's review process rather than the code