example-mcp-server-stdio

Instructions

Implementation Reference

• src/server.ts:636-747 (handler)

  Handler logic for 'solve_math_problem' tool. Parses the problem string to detect area calculations for basic shapes (rectangle, circle), uses elicitInput to request missing dimensions, computes area using basic arithmetic, returns formatted text response with optional step-by-step explanation, handles user cancellation and elicitInput errors.
  async ({ problem, showSteps }) => { log.info('Solving math problem'); requestCount++; // Check for ambiguous area problems if (problem.toLowerCase().includes('area') && !problem.match(/\d+/)) { // Determine shape type let shape = 'unknown'; if (problem.toLowerCase().includes('rectangle')) shape = 'rectangle'; else if (problem.toLowerCase().includes('circle')) shape = 'circle'; else if (problem.toLowerCase().includes('triangle')) shape = 'triangle'; if (shape === 'rectangle') { try { const result = await server.server.elicitInput({ message: 'I need the dimensions to calculate the area of a rectangle.', requestedSchema: { type: 'object', properties: { length: { type: 'number', description: 'Length of the rectangle' }, width: { type: 'number', description: 'Width of the rectangle' }, }, required: ['length', 'width'], }, }); if (result.action === 'accept') { const { length, width } = result.content as { length: number; width: number }; const area = length * width; const steps = showSteps ? `\n### Steps:\n1. Formula: Area = length × width\n2. Substitution: Area = ${length} × ${width}\n3. Calculation: Area = ${area}\n` : ''; return { content: [ { type: 'text', text: `## Area of Rectangle\n\nThe area is ${length} × ${width} = ${area} square units.${steps}`, }, ], }; } else { return { content: [{ type: 'text', text: 'Area calculation cancelled by user.' }] }; } } catch (e) { // NOTE: `elicitInput` can fail for several reasons: the transport // was closed, the request timed out, or the client explicitly // rejected the elicitation. We wrap this in a generic InternalError // because from the tool's perspective, its interactive flow was // unexpectedly interrupted. throw new McpError( ErrorCode.InternalError, 'Failed to complete interactive input with the user.', ); } } else if (shape === 'circle') { try { const result = await server.server.elicitInput({ message: 'I need the radius to calculate the area of a circle.', requestedSchema: { type: 'object', properties: { radius: { type: 'number', description: 'Radius of the circle' }, }, required: ['radius'], }, }); if (result.action === 'accept') { const { radius } = result.content as { radius: number }; const area = Math.PI * radius * radius; const steps = showSteps ? `\n### Steps:\n1. Formula: Area = π × r²\n2. Substitution: Area = π × ${radius}²\n3. Calculation: Area = ${area.toFixed(2)}\n` : ''; return { content: [ { type: 'text', text: `## Area of Circle\n\nThe area is π × ${radius}² = ${area.toFixed(2)} square units.${steps}`, }, ], }; } else { return { content: [{ type: 'text', text: 'Area calculation cancelled by user.' }] }; } } catch (e) { // NOTE: `elicitInput` can fail for several reasons: the transport // was closed, the request timed out, or the client explicitly // rejected the elicitation. We wrap this in a generic InternalError // because from the tool's perspective, its interactive flow was // unexpectedly interrupted. throw new McpError( ErrorCode.InternalError, 'Failed to complete interactive input with the user.', ); } } } // Default response for non-area or non-ambiguous problems return { content: [ { type: 'text', text: `## Solving: ${problem}\n\n` + `This problem would be solved using appropriate mathematical methods.\n` + `${showSteps ? '\n### Steps:\n1. Analyze the problem\n2. Identify key values\n3. Apply appropriate formula\n4. Calculate result\n' : ''}`, }, ], }; }, );
• src/server.ts:624-627 (schema)

  Input schema using Zod for the 'solve_math_problem' tool, defining required 'problem' string parameter and optional 'showSteps' boolean.
  const solveMathProblemInputSchema = { problem: z.string().describe('The math problem to solve'), showSteps: z.boolean().optional().describe('Show step-by-step solution'), };
• src/server.ts:629-635 (registration)

  Registration of the 'solve_math_problem' tool on the MCP server, specifying name, title, description, and input schema reference. The handler is provided inline immediately after.
  server.registerTool( 'solve_math_problem', { title: 'Solve Math Problem', description: 'Solve a word problem or mathematical expression (may request user input)', inputSchema: solveMathProblemInputSchema, },