Building custom connectors

connectors/building/index First recorded · 82 lines, first recorded

# Building custom connectors ## Getting started ### Key resources ## Transport & authentication ### Supported transports ### Authentication features ## Protocol features ### Supported ### Not yet supported ## Technical specifications ## Testing your server ## Related topics

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# Building custom connectors

> Build your own MCP servers to connect Claude to your tools and data

## Getting started

<Note>
  **Authentication is the most common stumbling block.** Before you build, read the [authentication reference](/docs/connectors/building/authentication)—Claude's auth support differs from the generic MCP spec in a few important ways.
</Note>

Not sure whether to build an MCP server, a plugin, or both? See [what to build](/docs/connectors/building/what-to-build).

<Tip>
  **Build with Claude.** Install the official [`mcp-server-dev` plugin](https://github.com/anthropics/claude-plugins-official/tree/main/plugins/mcp-server-dev) in Claude Code—it walks you through building, testing, and packaging an MCP server interactively, using these docs as its reference.
</Tip>

### Key resources

* **SDK Examples**: [TypeScript](https://github.com/modelcontextprotocol/typescript-sdk) and [Python](https://github.com/modelcontextprotocol/python-sdk) SDKs contain server implementation examples
* **Protocol Specification**: [modelcontextprotocol.io](https://modelcontextprotocol.io)
* **Hosting Solutions**: Platforms like Cloudflare offer remote MCP server hosting with autoscaling and OAuth management
* **Auth Specifications**: Review the [authorization spec](https://modelcontextprotocol.io/specification/latest/basic/authorization) with emphasis on third-party service flows

## Transport & authentication

### Supported transports

Claude supports both Streamable HTTP and the legacy HTTP+SSE transport. The legacy HTTP+SSE transport is being deprecated in favor of Streamable HTTP.

### Authentication features

* Supports the [2025-03-26](https://modelcontextprotocol.io/specification/2025-03-26/basic/authorization), [2025-06-18](https://modelcontextprotocol.io/specification/2025-06-18/basic/authorization), and [2025-11-25](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization) auth specifications
* Dynamic Client Registration (DCR) enabled
* OAuth callback: `https://claude.ai/api/mcp/auth_callback` (hosted surfaces); loopback redirect for Claude Code — see [callback URLs](/docs/connectors/building/authentication#callback-urls)
* Token refresh and expiry support
* Custom credentials for non-DCR servers

## Protocol features

### Supported

* [Tools](https://modelcontextprotocol.io/specification/latest/server/tools), [prompts](https://modelcontextprotocol.io/specification/latest/server/prompts), and [resources](https://modelcontextprotocol.io/specification/latest/server/resources)
* [Text](https://modelcontextprotocol.io/specification/latest/schema#textcontent) and [image-based](https://modelcontextprotocol.io/specification/latest/server/tools#image-content) tool results
* [Text](https://modelcontextprotocol.io/specification/latest/schema#textresourcecontents) and [binary](https://modelcontextprotocol.io/specification/latest/schema#blobresourcecontents) resources

### Not yet supported

* Resource subscriptions
* Sampling
* Advanced/draft capabilities

## Technical specifications

| Constraint                             | Limit                                                    |
| -------------------------------------- | -------------------------------------------------------- |
| Claude.ai/Desktop max tool result size | \~150,000 characters                                     |
| Claude Code max tool result size       | 25,000 tokens (configurable via `MAX_MCP_OUTPUT_TOKENS`) |
| Claude Code timeout                    | Configurable via `MCP_TOOL_TIMEOUT`                      |
| Claude.ai/Desktop timeout              | 300 seconds (5 minutes)                                  |
| Transport protocol                     | Streamable HTTP (legacy HTTP+SSE being deprecated)       |

## Testing your server

1. Add directly to Claude via **Customize > Connectors**
2. Use the [MCP inspector](https://modelcontextprotocol.io/docs/tools/inspector) to validate auth flows
3. Add to Claude Code with `claude mcp add` and check `/mcp` for status. See the [Claude Code MCP quickstart](https://code.claude.com/docs/en/mcp-quickstart).

## Related topics

<Columns cols={2}>
  <Card title="MCP Overview" icon="plug" href="/docs/connectors/building/mcp">
    Understanding the Model Context Protocol.
  </Card>

  <Card title="Submit to Directory" icon="paper-plane" href="/docs/connectors/building/submission">
    Review requirements and submit your connector.
  </Card>

  <Card title="Test in Claude Code" icon="terminal" href="https://code.claude.com/docs/en/mcp">
    Connect and debug your server with the Claude Code CLI.
  </Card>
</Columns>