Google Cloud MCP Server

Implementation Reference

• src/services/spanner/tools.ts:60-126 (handler)

  The core handler function for the 'execute-spanner-query' tool. It handles input parameters, retrieves the Google Cloud project ID, configures and initializes the Spanner client, executes the SQL query with optional parameters, processes the results, formats them into a markdown table (limiting to 100 rows), and returns the output as structured text content. Includes error handling.
  async ({ sql, instanceId, databaseId, params }, _extra) => { try { const projectId = await getProjectId(); const config = await getSpannerConfig( Array.isArray(instanceId) ? instanceId[0] : instanceId, Array.isArray(databaseId) ? databaseId[0] : databaseId ); const spanner = await getSpannerClient(); console.log(`Using Spanner client with project ID: ${spanner.projectId} for execute-spanner-query`); const instance = spanner.instance(config.instanceId); const database = instance.database(config.databaseId); // Execute the query const [result] = await database.run({ sql, params: params || {} }); if (!result || result.length === 0) { return { content: [{ type: 'text', text: `# Query Results\n\nProject: ${projectId}\nInstance: ${config.instanceId}\nDatabase: ${config.databaseId}\n\nQuery executed successfully. No results returned.` }] }; } // Convert to markdown table const columns = Object.keys(result[0]); let markdown = `# Query Results\n\nProject: ${projectId}\nInstance: ${config.instanceId}\nDatabase: ${config.databaseId}\n\n`; markdown += `SQL: \`${sql}\`\n\n`; markdown += `Rows: ${result.length}\n\n`; // Table header markdown += '| ' + columns.join(' | ') + ' |\n'; markdown += '| ' + columns.map(() => '---').join(' | ') + ' |\n'; // Table rows (limit to 100 rows for display) const displayRows = result.slice(0, 100); for (const row of displayRows) { const rowValues = columns.map(col => { const value = (row as any)[col]; if (value === null || value === undefined) return 'NULL'; if (typeof value === 'object') return JSON.stringify(value); return String(value); }); markdown += '| ' + rowValues.join(' | ') + ' |\n'; } if (result.length > 100) { markdown += '\n*Results truncated. Showing 100 of ' + result.length + ' rows.*'; } return { content: [{ type: 'text', text: markdown }] }; } catch (error: any) { console.error('Error executing Spanner query:', error); throw error; } }
• src/services/spanner/tools.ts:54-59 (schema)

  The Zod input schema for the 'execute-spanner-query' tool, defining required 'sql' string and optional 'instanceId', 'databaseId', and 'params' fields with descriptions.
  { sql: z.string().describe('The SQL query to execute'), instanceId: z.string().optional().describe('Spanner instance ID (defaults to SPANNER_INSTANCE env var)'), databaseId: z.string().optional().describe('Spanner database ID (defaults to SPANNER_DATABASE env var)'), params: z.record(z.any()).optional().describe('Query parameters') },
• src/services/spanner/tools.ts:52-127 (registration)

  The registration of the 'execute-spanner-query' tool using server.tool(), including the tool name, input schema, and handler function within the registerSpannerTools export.
  server.tool( 'execute-spanner-query', { sql: z.string().describe('The SQL query to execute'), instanceId: z.string().optional().describe('Spanner instance ID (defaults to SPANNER_INSTANCE env var)'), databaseId: z.string().optional().describe('Spanner database ID (defaults to SPANNER_DATABASE env var)'), params: z.record(z.any()).optional().describe('Query parameters') }, async ({ sql, instanceId, databaseId, params }, _extra) => { try { const projectId = await getProjectId(); const config = await getSpannerConfig( Array.isArray(instanceId) ? instanceId[0] : instanceId, Array.isArray(databaseId) ? databaseId[0] : databaseId ); const spanner = await getSpannerClient(); console.log(`Using Spanner client with project ID: ${spanner.projectId} for execute-spanner-query`); const instance = spanner.instance(config.instanceId); const database = instance.database(config.databaseId); // Execute the query const [result] = await database.run({ sql, params: params || {} }); if (!result || result.length === 0) { return { content: [{ type: 'text', text: `# Query Results\n\nProject: ${projectId}\nInstance: ${config.instanceId}\nDatabase: ${config.databaseId}\n\nQuery executed successfully. No results returned.` }] }; } // Convert to markdown table const columns = Object.keys(result[0]); let markdown = `# Query Results\n\nProject: ${projectId}\nInstance: ${config.instanceId}\nDatabase: ${config.databaseId}\n\n`; markdown += `SQL: \`${sql}\`\n\n`; markdown += `Rows: ${result.length}\n\n`; // Table header markdown += '| ' + columns.join(' | ') + ' |\n'; markdown += '| ' + columns.map(() => '---').join(' | ') + ' |\n'; // Table rows (limit to 100 rows for display) const displayRows = result.slice(0, 100); for (const row of displayRows) { const rowValues = columns.map(col => { const value = (row as any)[col]; if (value === null || value === undefined) return 'NULL'; if (typeof value === 'object') return JSON.stringify(value); return String(value); }); markdown += '| ' + rowValues.join(' | ') + ' |\n'; } if (result.length > 100) { markdown += '\n*Results truncated. Showing 100 of ' + result.length + ' rows.*'; } return { content: [{ type: 'text', text: markdown }] }; } catch (error: any) { console.error('Error executing Spanner query:', error); throw error; } } );
• src/index.ts:140-140 (registration)

  Invocation of registerSpannerTools(server) in the main server setup, which registers the execute-spanner-query tool among others.
  registerSpannerTools(server);