How to Connect Your Twilio Agent to External APIs in Node.js

Twilio’s Node.js tutorial shows how to build a voice-enabled AI agent that uses Conversation Relay, OpenAI tool calling, and an external REST API to provide live information during phone conversations. The example creates a cat-fact agent: Express and WebSocket routes connect an incoming Twilio call to Conversation Relay, while a handler records caller prompts, manages interruptions, and streams responses. OpenAI is configured with a system prompt and a function schema requiring the model to call a `get_cat_fact` tool rather than inventing information; the tool fetches a random fact from the Cat Facts API and returns it to the model for a natural spoken reply. Developers need a Twilio account and voice number, Node.js 18 or later, an OpenAI API key, and ngrok to expose the local application, then configure the Twilio number’s incoming-call webhook to the public `/voice` endpoint. The tutorial also notes troubleshooting steps for webhook URLs, API credentials, external API authentication, and Node.js fetch support, and frames the pattern as a basis for agents that can retrieve customer information, inventory, calendars, and other real-time data.

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