> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hasmcp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# What is the endpoint to add a tool to an MCP server?

> API reference identifying the exact POST endpoint and payload structure for creating Server-to-Tool associations.

# Defining the Tool Association Endpoint

The core mechanism for extending an MCP server's execution capabilities is securely linking it to pre-defined Provider Tools.

## The API Endpoint

To authorize new tool access for a specific server, use the highly specific `POST` routing path built around the server's unique identifier.

**`POST /servers/{serverId}/tools`**

* `{serverId}` dictates the 11-character hash indicating the specific agent environment.

### Structuring the Association

Because tools belong to specific API integrations, the [`CreateServerToolRequest`](/api-reference/servers/tools/create-mcp-server-tool-association) mandates passing an object defining the entire triangular relationship. You cannot simply pass the tool ID; you must also declare `providerID` and `serverID` inside the payload object.

```json theme={null}
{
 "tool": {
 "serverID": "sE8vKd2qLp9",
 "providerID": "kSuB9Gf6aD4",
 "toolID": "tH4mZw9xV2n"
 }
}
```

### Successful Response

The command yields `200 OK` upon success, replying with the mapped [`CreateServerToolResponse`](/api-reference/servers/tools/create-mcp-server-tool-association) object. The server immediately begins reporting this new tool structure in its `ListTools` protocol handler to downstream LLM inferences.