> For the complete documentation index, see [llms.txt](https://alhena.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alhena.gitbook.io/docs/integrations/custom-extensions.md).

# Custom Extensions

Build custom integrations to connect your AI agents to any external service. Custom extensions let agents access real-time data, execute actions, and integrate with systems not covered by built-in integrations.

## Extension Types

| Type                                                                 | Description                                                 | Plan |
| -------------------------------------------------------------------- | ----------------------------------------------------------- | ---- |
| [API Tools](/docs/integrations/custom-extensions/api-tools.md)       | Make HTTP requests to external services                     | Pro  |
| [MCP Servers](/docs/integrations/custom-extensions/mcp-servers.md)   | Connect via Model Context Protocol for complex integrations | Pro  |
| [Sheet Search](/docs/integrations/custom-extensions/sheet-search.md) | Search spreadsheet data in your knowledge base              | All  |

## When to Use Each Extension

**Use API Tools when:**

* You need to call a REST API endpoint
* The integration is straightforward request/response
* You're connecting to a single service

**Use MCP Servers when:**

* You need multiple related tools from one service
* You want to use pre-built MCP connectors (like Zapier)
* You're building complex integrations with programmatic control

**Use Sheet Search when:**

* Your data is in spreadsheets
* You need real-time access to tabular data
* Product catalogs, pricing tables, or structured lookups