modelcontextprotocol/inspector
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Cliff Hall 2025-05-30 18:39:01 -04:00 • committed by GitHub
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10
README.md
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@ -10,6 +10,16 @@ The MCP inspector is a developer tool for testing and debugging MCP servers.
- Node.js: ^22.7.5
### Quick Start (UI mode)
To get up and running right away with the UI, just execute the following:
```bash
npx @modelcontextprotocol/inspector
```
The server will start up and the UI will be accessible at `http://localhost:6274`.
### From an MCP server repository
To inspect an MCP server implementation, there's no need to clone this repo. Instead, use `npx`. For example, if your server is built at `build/index.js`:

58
server/src/index.ts
View file

@ -86,7 +86,8 @@ app.use((req, res, next) => {
next();
});
const webAppTransports: Map<string, Transport> = new Map<string, Transport>(); // Transports by sessionId
const webAppTransports: Map<string, Transport> = new Map<string, Transport>(); // Web app transports by web app sessionId
const serverTransports: Map<string, Transport> = new Map<string, Transport>(); // Server Transports by web app sessionId
const createTransport = async (req: express.Request): Promise<Transport> => {
const query = req.query;
@ -154,8 +155,6 @@ const createTransport = async (req: express.Request): Promise<Transport> => {
}
};
let backingServerTransport: Transport | undefined;
app.get("/mcp", async (req, res) => {
const sessionId = req.headers["mcp-session-id"] as string;
console.log(`Received GET message for sessionId ${sessionId}`);
@ -178,12 +177,12 @@ app.get("/mcp", async (req, res) => {
app.post("/mcp", async (req, res) => {
const sessionId = req.headers["mcp-session-id"] as string | undefined;
console.log(`Received POST message for sessionId ${sessionId}`);
let serverTransport: Transport | undefined;
if (!sessionId) {
try {
console.log("New streamable-http connection");
try {
await backingServerTransport?.close();
backingServerTransport = await createTransport(req);
serverTransport = await createTransport(req);
} catch (error) {
if (error instanceof SseError && error.code === 401) {
console.error(
@ -197,12 +196,13 @@ app.post("/mcp", async (req, res) => {
throw error;
}
console.log("Connected MCP client to backing server transport");
console.log("Connected MCP client to server transport");
const webAppTransport = new StreamableHTTPServerTransport({
sessionIdGenerator: randomUUID,
onsessioninitialized: (sessionId) => {
webAppTransports.set(sessionId, webAppTransport);
serverTransports.set(sessionId, serverTransport!);
console.log("Created streamable web app transport " + sessionId);
},
});
@ -211,7 +211,7 @@ app.post("/mcp", async (req, res) => {
mcpProxy({
transportToClient: webAppTransport,
transportToServer: backingServerTransport,
transportToServer: serverTransport,
});
await (webAppTransport as StreamableHTTPServerTransport).handleRequest(
@ -246,10 +246,9 @@ app.post("/mcp", async (req, res) => {
app.get("/stdio", async (req, res) => {
try {
console.log("New connection");
let serverTransport: Transport | undefined;
try {
await backingServerTransport?.close();
backingServerTransport = await createTransport(req);
serverTransport = await createTransport(req);
} catch (error) {
if (error instanceof SseError && error.code === 401) {
console.error(
@ -267,26 +266,24 @@ app.get("/stdio", async (req, res) => {
const webAppTransport = new SSEServerTransport("/message", res);
webAppTransports.set(webAppTransport.sessionId, webAppTransport);
console.log("Created web app transport");
serverTransports.set(webAppTransport.sessionId, serverTransport);
console.log("Created client/server transports");
await webAppTransport.start();
(backingServerTransport as StdioClientTransport).stderr!.on(
"data",
(chunk) => {
webAppTransport.send({
jsonrpc: "2.0",
method: "notifications/stderr",
params: {
content: chunk.toString(),
},
});
},
);
(serverTransport as StdioClientTransport).stderr!.on("data", (chunk) => {
webAppTransport.send({
jsonrpc: "2.0",
method: "notifications/stderr",
params: {
content: chunk.toString(),
},
});
});
mcpProxy({
transportToClient: webAppTransport,
transportToServer: backingServerTransport,
transportToServer: serverTransport,
});
console.log("Set up MCP proxy");
@ -301,10 +298,9 @@ app.get("/sse", async (req, res) => {
console.log(
"New SSE connection. NOTE: The sse transport is deprecated and has been replaced by streamable-http",
);
let serverTransport: Transport | undefined;
try {
await backingServerTransport?.close();
backingServerTransport = await createTransport(req);
serverTransport = await createTransport(req);
} catch (error) {
if (error instanceof SseError && error.code === 401) {
console.error(
@ -322,13 +318,15 @@ app.get("/sse", async (req, res) => {
const webAppTransport = new SSEServerTransport("/message", res);
webAppTransports.set(webAppTransport.sessionId, webAppTransport);
console.log("Created web app transport");
console.log("Created client transport");
serverTransports.set(webAppTransport.sessionId, serverTransport);
console.log("Created server transport");
await webAppTransport.start();
mcpProxy({
transportToClient: webAppTransport,
transportToServer: backingServerTransport,
transportToServer: serverTransport,
});
console.log("Set up MCP proxy");