Tool calling for AI agents

AI agents become useful when they can act in the systems your users already use: HubSpot, Gmail, Slack, Linear, Notion, Salesforce, and the rest. The hard part is not just calling an API. It is OAuth, token refresh, per-user permissions, rate limits, logging, and keeping credentials out of the model loop. Nango handles that plumbing. Users authorize integrations through Nango, you choose which tools to expose, and agents call them through the agent sessions API.

When this fits

Use Nango for AI tool calling when:

• Your agent needs to fetch or change data in external APIs.
• Tool calls must run with each user’s own credentials.
• You want logs, retries, rate-limit handling, and a deployable runtime.
• You need a catalog of tools for agentic tool calling now, with room for custom tools later.
• You want one MCP server URL for Nango-hosted tools.

For RAG-style workflows where data should be replicated before the agent needs it, use Sync external API data.

How Nango fits in

1. Your user authorizes an integration with Nango.
2. You use catalog tools directly or deploy custom tools for allowed operations.
3. Your agent discovers the available tools.
4. The agent asks Nango to execute a tool for the right connection.
5. Nango runs the external API call with the user’s credentials and logs the execution.

This keeps provider credentials in Nango and gives you a common tool surface across frameworks.

Technical setup

Nango supports both direct tool execution and MCP-based tool discovery through agent sessions.

What to read next

• Tool calling & MCP - connect Nango tools to agents, LLM SDKs, and MCP clients.
• Tools - build the tools agents can call.
• List functions - list available functions programmatically.
• Functions guide - create, test, deploy, and trigger functions.
• Auth guide - let users authorize external APIs.