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

# Custom Tools

> Extend Claude Code with custom tools via plugins and MCP.

You can add custom tools to Claude Code through two mechanisms: the **plugin system** (for tools bundled directly into Claude Code's runtime) and **MCP servers** (for tools exposed by external processes).

## Adding tools via MCP (recommended)

The easiest way to give Claude new capabilities is through an MCP server. MCP tools appear in Claude's tool list just like built-in tools.

**Advantages:**

* No changes to Claude Code itself
* Works with any language (Node.js, Python, Go, Rust, etc.)
* Hot-reloadable without restarting Claude Code
* Shareable across teams via a central MCP server

See [MCP Protocol](/advanced/mcp-protocol) for a complete guide to building MCP servers.

## Adding tools via plugins

Plugins can register tools that run inside the Claude Code process. This is useful for tools that need deep integration with Claude Code's internals.

Create a plugin in `~/.claude/plugins/my-plugin/`:

```
my-plugin/
├── manifest.json
├── index.js
└── tools/
    └── myCustomTool.js
```

**manifest.json:**

```json theme={null}
{
  "name": "my-plugin",
  "version": "1.0.0",
  "tools": ["tools/myCustomTool.js"]
}
```

**tools/myCustomTool.js:**

```javascript theme={null}
module.exports = {
  name: "my_custom_tool",
  description: "Does something custom",
  inputSchema: {
    type: "object",
    properties: {
      input: { type: "string", description: "The input value" }
    },
    required: ["input"]
  },
  async call({ input }) {
    // Tool implementation
    return { output: `Processed: ${input}` };
  }
};
```

Reload after adding:

```
> /reload-plugins
```

## Tool input schemas

All tools — built-in, plugin, and MCP — use JSON Schema for their input definitions. Claude uses these schemas to generate valid inputs.

**Schema best practices:**

* Write clear `description` fields — Claude uses them to decide when to use the tool
* Use `required` to mark mandatory fields
* Use `enum` to constrain allowed values
* Add `default` values where appropriate

## AskUserQuestionTool

Claude Code also has an `AskUserQuestionTool` for tools that need to interactively ask the user for input mid-execution. Custom tools can trigger this pattern by returning a question response that Claude translates into a user prompt.

<Tip>
  For most use cases, MCP is the better choice for custom tools. The plugin API is more powerful but more complex, and it requires familiarity with Claude Code's internals.
</Tip>