claude-code-best/packages/builtin-tools/src/tools/MCPTool/MCPTool.ts

import { z } from 'zod/v4'
import { buildTool, type ToolDef } from 'src/Tool.js'
import { lazySchema } from 'src/utils/lazySchema.js'
import type { PermissionResult } from 'src/utils/permissions/PermissionResult.js'
import { isOutputLineTruncated } from 'src/utils/terminal.js'
import { DESCRIPTION, PROMPT } from './prompt.js'
import {
  renderToolResultMessage,
  renderToolUseMessage,
  renderToolUseProgressMessage,
} from './UI.js'

// Allow any input object since MCP tools define their own schemas
export const inputSchema = lazySchema(() => z.object({}).passthrough())
type InputSchema = ReturnType<typeof inputSchema>

export const outputSchema = lazySchema(() =>
  z.string().describe('MCP tool execution result'),
)
type OutputSchema = ReturnType<typeof outputSchema>

export type Output = z.infer<OutputSchema>

// Re-export MCPProgress from centralized types to break import cycles
export type { MCPProgress } from 'src/types/tools.js'

export const MCPTool = buildTool({
  isMcp: true,
  // Overridden in mcpClient.ts with the real MCP tool name + args
  isOpenWorld() {
    return false
  },
  // Overridden in mcpClient.ts
  name: 'mcp',
  maxResultSizeChars: 100_000,
  // Overridden in mcpClient.ts
  async description() {
    return DESCRIPTION
  },
  // Overridden in mcpClient.ts
  async prompt() {
    return PROMPT
  },
  get inputSchema(): InputSchema {
    return inputSchema()
  },
  get outputSchema(): OutputSchema {
    return outputSchema()
  },
  // Overridden in mcpClient.ts
  async call() {
    return {
      data: '',
    }
  },
  async checkPermissions(): Promise<PermissionResult> {
    return {
      behavior: 'passthrough',
      message: 'MCPTool requires permission.',
    }
  },
  renderToolUseMessage,
  // Overridden in mcpClient.ts
  userFacingName: () => 'mcp',
  renderToolUseProgressMessage,
  renderToolResultMessage,
  isResultTruncated(output: Output): boolean {
    return isOutputLineTruncated(output)
  },
  mapToolResultToToolResultBlockParam(content, toolUseID) {
    return {
      tool_use_id: toolUseID,
      type: 'tool_result',
      content,
    }
  },
} satisfies ToolDef<InputSchema, Output>)