feat: add transport option to cli

Author: ryanjclark

cli/src/index.ts

@@ -29,9 +29,13 @@ type Args = {
   logLevel?: LogLevel;
   toolName?: string;
   toolArg?: Record<string, string>;
+  transport?: "sse" | "stdio" | "http";
 };
 
-function createTransportOptions(target: string[]): TransportOptions {
+function createTransportOptions(
+  target: string[],
+  transport?: "sse" | "stdio" | "http",
+): TransportOptions {
   if (target.length === 0) {
     throw new Error(
       "Target is required. Specify a URL or a command to execute.",
@@ -50,16 +54,38 @@ function createTransportOptions(target: string[]): TransportOptions {
     throw new Error("Arguments cannot be passed to a URL-based MCP server.");
   }
 
+  let transportType: "sse" | "stdio" | "http";
+  if (transport) {
+    if (!isUrl && transport !== "stdio") {
+      throw new Error("Only stdio transport can be used with local commands.");
+    }
+    if (isUrl && transport === "stdio") {
+      throw new Error("stdio transport cannot be used with URLs.");
+    }
+    transportType = transport;
+  } else if (isUrl) {
+    const url = new URL(command);
+    if (url.pathname.endsWith("/mcp")) {
+      transportType = "http";
+    } else if (url.pathname.endsWith("/sse")) {
+      transportType = "sse";
+    } else {
+      transportType = "sse";
+    }
+  } else {
+    transportType = "stdio";
+  }
+
   return {
-    transportType: isUrl ? "sse" : "stdio",
+    transportType,
     command: isUrl ? undefined : command,
     args: isUrl ? undefined : commandArgs,
     url: isUrl ? command : undefined,
   };
 }
 
 async function callMethod(args: Args): Promise<void> {
-  const transportOptions = createTransportOptions(args.target);
+  const transportOptions = createTransportOptions(args.target, args.transport);
   const transport = createTransport(transportOptions);
   const client = new Client({
     name: "inspector-cli",
@@ -214,6 +240,22 @@ function parseArgs(): Args {
 
         return value as LogLevel;
       },
+    )
+    //
+    // Transport options
+    //
+    .option(
+      "--transport <type>",
+      "Transport type (sse, http, or stdio). Auto-detected from URL: /mcp → http, /sse → sse, commands → stdio",
+      (value: string) => {
+        const validTransports = ["sse", "http", "stdio"];
+        if (!validTransports.includes(value)) {
+          throw new Error(
+            `Invalid transport type: ${value}. Valid types are: ${validTransports.join(", ")}`,
+          );
+        }
+        return value as "sse" | "http" | "stdio";
+      },
     );
 
   // Parse only the arguments before --

cli/src/transport.ts

@@ -3,23 +3,35 @@ import {
   getDefaultEnvironment,
   StdioClientTransport,
 } from "@modelcontextprotocol/sdk/client/stdio.js";
+import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";
 import type { Transport } from "@modelcontextprotocol/sdk/shared/transport.js";
 import { findActualExecutable } from "spawn-rx";
 
 export type TransportOptions = {
-  transportType: "sse" | "stdio";
+  transportType: "sse" | "stdio" | "http";
   command?: string;
   args?: string[];
   url?: string;
 };
 
 function createSSETransport(options: TransportOptions): Transport {
   const baseUrl = new URL(options.url ?? "");
-  const sseUrl = new URL("/sse", baseUrl);
+  const sseUrl = baseUrl.pathname.endsWith("/sse")
+    ? baseUrl
+    : new URL("/sse", baseUrl);
 
   return new SSEClientTransport(sseUrl);
 }
 
+function createHTTPTransport(options: TransportOptions): Transport {
+  const baseUrl = new URL(options.url ?? "");
+  const mcpUrl = baseUrl.pathname.endsWith("/mcp")
+    ? baseUrl
+    : new URL("/mcp", baseUrl);
+
+  return new StreamableHTTPClientTransport(mcpUrl);
+}
+
 function createStdioTransport(options: TransportOptions): Transport {
   let args: string[] = [];
 
@@ -67,6 +79,10 @@ export function createTransport(options: TransportOptions): Transport {
       return createSSETransport(options);
     }
 
+    if (transportType === "http") {
+      return createHTTPTransport(options);
+    }
+
     throw new Error(`Unsupported transport type: ${transportType}`);
   } catch (error) {
     throw new Error(