Google Cloud MCP Server

Implementation Reference

• src/services/spanner/tools.ts:216-291 (handler)

  The handler function that implements the core logic of listing Spanner instances. It retrieves the project ID from various sources, creates a Spanner client, fetches the list of instances, formats them into a Markdown table with metadata, and includes navigation resource URIs.
  async (_params, _extra) => { try { // First try to get the project ID from the state manager let projectId = stateManager.getCurrentProjectId(); if (projectId) { console.log(`Got project ID from state manager: ${projectId}`); } else { // If not in state manager, try to get it from environment const envProjectId = process.env.GOOGLE_CLOUD_PROJECT; if (envProjectId) { projectId = envProjectId; console.log(`Got project ID from environment: ${projectId}`); // Store in state manager for future use await stateManager.setCurrentProjectId(projectId); } else { // If not in environment, try to get it from our function projectId = await getProjectId(); console.log(`Got project ID from getProjectId: ${projectId}`); } } if (!projectId) { throw new Error('Project ID could not be determined. Please set a project ID using the set-project-id tool.'); } // Create Spanner client with explicit project ID const spanner = new (await import('@google-cloud/spanner')).Spanner({ projectId: projectId }); console.log(`Using Spanner client with explicit project ID: ${projectId} for list-spanner-instances`); const [instances] = await spanner.getInstances(); if (!instances || instances.length === 0) { return { content: [{ type: 'text', text: `# Spanner Instances\n\nProject: ${projectId}\n\nNo instances found in the project.` }] }; } let markdown = `# Spanner Instances\n\nProject: ${projectId}\n\n`; // Table header markdown += '| Instance ID | State | Config | Nodes |\n'; markdown += '|-------------|-------|--------|-------|\n'; // Table rows for (const instance of instances) { const metadata = instance.metadata || {}; markdown += `| ${instance.id || 'unknown'} | ${metadata.state || 'unknown'} | ${metadata.config?.split('/').pop() || 'unknown'} | ${metadata.nodeCount || 'unknown'} |\n`; } // Add resource links for further exploration markdown += '\n## Available Resources\n\n'; markdown += `- All Instances: \`gcp-spanner://${projectId}/instances\`\n`; for (const instance of instances) { markdown += `- Databases in ${instance.id}: \`gcp-spanner://${projectId}/${instance.id}/databases\`\n`; } return { content: [{ type: 'text', text: markdown }] }; } catch (error: any) { console.error('Error listing Spanner instances:', error); throw error; } }
• src/services/spanner/tools.ts:211-215 (schema)

  The Zod input schema for the list-spanner-instances tool. It defines an optional dummy string parameter to maintain compatibility with MCP clients that expect an input object.
  // Define an empty schema with a dummy parameter that's optional // This ensures compatibility with clients that expect an object parameter { _dummy: z.string().optional().describe('Not used, just to ensure parameter compatibility') },
• src/services/spanner/tools.ts:209-292 (registration)

  The server.tool() call that registers the 'list-spanner-instances' tool on the MCP server, specifying its name, input schema, and handler function.
  server.tool( 'list-spanner-instances', // Define an empty schema with a dummy parameter that's optional // This ensures compatibility with clients that expect an object parameter { _dummy: z.string().optional().describe('Not used, just to ensure parameter compatibility') }, async (_params, _extra) => { try { // First try to get the project ID from the state manager let projectId = stateManager.getCurrentProjectId(); if (projectId) { console.log(`Got project ID from state manager: ${projectId}`); } else { // If not in state manager, try to get it from environment const envProjectId = process.env.GOOGLE_CLOUD_PROJECT; if (envProjectId) { projectId = envProjectId; console.log(`Got project ID from environment: ${projectId}`); // Store in state manager for future use await stateManager.setCurrentProjectId(projectId); } else { // If not in environment, try to get it from our function projectId = await getProjectId(); console.log(`Got project ID from getProjectId: ${projectId}`); } } if (!projectId) { throw new Error('Project ID could not be determined. Please set a project ID using the set-project-id tool.'); } // Create Spanner client with explicit project ID const spanner = new (await import('@google-cloud/spanner')).Spanner({ projectId: projectId }); console.log(`Using Spanner client with explicit project ID: ${projectId} for list-spanner-instances`); const [instances] = await spanner.getInstances(); if (!instances || instances.length === 0) { return { content: [{ type: 'text', text: `# Spanner Instances\n\nProject: ${projectId}\n\nNo instances found in the project.` }] }; } let markdown = `# Spanner Instances\n\nProject: ${projectId}\n\n`; // Table header markdown += '| Instance ID | State | Config | Nodes |\n'; markdown += '|-------------|-------|--------|-------|\n'; // Table rows for (const instance of instances) { const metadata = instance.metadata || {}; markdown += `| ${instance.id || 'unknown'} | ${metadata.state || 'unknown'} | ${metadata.config?.split('/').pop() || 'unknown'} | ${metadata.nodeCount || 'unknown'} |\n`; } // Add resource links for further exploration markdown += '\n## Available Resources\n\n'; markdown += `- All Instances: \`gcp-spanner://${projectId}/instances\`\n`; for (const instance of instances) { markdown += `- Databases in ${instance.id}: \`gcp-spanner://${projectId}/${instance.id}/databases\`\n`; } return { content: [{ type: 'text', text: markdown }] }; } catch (error: any) { console.error('Error listing Spanner instances:', error); throw error; } } );
• src/index.ts:140-140 (registration)

  Invocation of registerSpannerTools in the main server initialization, which registers all Spanner tools including list-spanner-instances.
  registerSpannerTools(server);