MCP Client Patterns

MCP Client Patterns

HTTP JSON-RPC Call (simple, no SDK needed)

async function callMcpTool(
  serverUrl: string,
  toolName: string,
  args: Record<string, unknown>
): Promise<string> {
  const response = await fetch(`${serverUrl}/mcp`, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      jsonrpc: '2.0',
      id: Date.now(),
      method: 'tools/call',
      params: { name: toolName, arguments: args }
    }),
    signal: AbortSignal.timeout(30_000),  // 30s timeout
  });
  const data = await response.json();
  if (data.error) throw new Error(data.error.message);
  return data.result?.content?.[0]?.text ?? '';
}

// Usage
const summary = await callMcpTool(
  'http://localhost:3003',
  'claude_summarize',
  { content: longText, format: 'bullets' }
);

List Available Tools

const response = await fetch(`${serverUrl}/mcp`, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ jsonrpc: '2.0', id: 1, method: 'tools/list', params: {} })
});
const { result } = await response.json();
console.log(result.tools.map(t => t.name));

Julia's MCP Call Map