To connect to an MCP server, first identify where it runs and which transport it supports. Use stdio when your MCP client launches a local server process. Use Streamable HTTP when the server is available at a remote MCP endpoint. Use legacy HTTP+SSE only when the server does not support Streamable HTTP and your client provides that compatibility path.
The connection itself is a protocol handshake: your client creates a transport, passes it to an MCP client object, and calls connect() (or enters the equivalent lifecycle in another SDK). After that succeeds, inspect the server’s capabilities and call its tools, resources, or prompts.
Choose the transport before configuring anything
The server’s location and advertised transport determine the setup values. Do not assume that a configuration copied from one host or SDK will work in another; menu names and file locations are host-specific.
| Connection choice | When to use it | What you configure | Typical failure |
|---|---|---|---|
| Local stdio | The client starts a server as a child process on the same machine. | Executable command and arguments. | The command is missing from the host’s PATH or the process exits during startup. |
| Remote Streamable HTTP | The server runs behind an HTTP MCP endpoint. | Endpoint URL and, where required, authorization. | Wrong endpoint, transport mismatch, or an authorization challenge. |
| Legacy HTTP+SSE | The remote server supports SSE but not Streamable HTTP. | The SSE endpoint and a client with legacy SSE support. | A client attempts only Streamable HTTP, or the server is not actually SSE-enabled. |
What stdio means
With stdio, the host owns the server process. It launches the configured executable, writes MCP messages to standard input, and reads responses from standard output. The server must be a command the host can execute, not merely a command that works in your interactive shell.
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What Streamable HTTP means
With Streamable HTTP, your client connects to a server URL instead of launching a local child process. The endpoint may protect requests with an authorization flow, so an access token is not always something you can safely paste into a static configuration file.
Why SSE is a fallback
HTTP+SSE is a compatibility option for older servers. For a new remote integration, prefer Streamable HTTP when the server supports it. A documented TypeScript flow tries Streamable HTTP first and retries with SSE using a fresh client when necessary.
Prepare the client and server
- Confirm the server’s transport documentation: stdio, Streamable HTTP, or legacy SSE.
- For stdio, verify the command and every argument in the same environment used by the host. A graphical host may have a different PATH from your terminal.
- For HTTP, record the complete MCP endpoint URL and determine whether the server requires authorization.
- Install the SDK version your project targets. The current TypeScript v2 package is installed with
npm install @modelcontextprotocol/client; package APIs are version-sensitive, so check the guide for your installed release. - Make sure the server is running, or that the host has permission to launch it, before testing a tool call.
Connect with the TypeScript SDK
The TypeScript pattern is the same for both transports: instantiate Client, instantiate the matching transport, pass that transport to connect(), then use the client after the promise resolves. The handshake negotiates the protocol version and exposes server capabilities and instructions.
Local server over stdio
import { Client } from '@modelcontextprotocol/client';
import { StdioClientTransport } from '@modelcontextprotocol/client/stdio.js';
const client = new Client({
name: 'example-client',
version: '1.0.0'
});
const transport = new StdioClientTransport({
command: 'node',
args: ['/absolute/path/to/server.js']
});
try {
await client.connect(transport);
const tools = await client.listTools();
console.log(tools);
} finally {
await client.close();
}Replace node and the script path with the server’s actual launcher. If the server is a Python executable, configure that executable and its arguments instead. Use absolute paths while diagnosing environment problems.
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import { Client } from '@modelcontextprotocol/client';
import { StreamableHTTPClientTransport } from '@modelcontextprotocol/client/http.js';
const client = new Client({
name: 'example-client',
version: '1.0.0'
});
const transport = new StreamableHTTPClientTransport(
new URL('https://example.com/mcp')
);
try {
await client.connect(transport);
console.log(await client.listTools());
} finally {
await client.close();
}Use the exact endpoint supplied by the server operator. If it requires OAuth, let the host or SDK perform the documented authorization flow rather than inventing a bearer-token configuration.
Attempt Streamable HTTP, then fall back to SSE
A failed HTTP attempt must not be reused blindly for the fallback. Create a fresh client and transport for the SSE connection, following the server’s documented SSE endpoint and your SDK release’s API.
import { Client } from '@modelcontextprotocol/client';
import { StreamableHTTPClientTransport } from '@modelcontextprotocol/client/http.js';
import { SSEClientTransport } from '@modelcontextprotocol/client/sse.js';
async function connectWithCompatibility(endpoint: string) {
let client = new Client({ name: 'example-client', version: '1.0.0' });
try {
await client.connect(
new StreamableHTTPClientTransport(new URL(endpoint))
);
return client;
} catch (httpError) {
await client.close().catch(() => {});
client = new Client({ name: 'example-client', version: '1.0.0' });
await client.connect(new SSEClientTransport(new URL(endpoint)));
return client;
}
}
const client = await connectWithCompatibility('https://example.com/mcp');
console.log(await client.listTools());
await client.close();Only use this fallback when your server and SDK document SSE support. An HTTP error caused by bad credentials or a wrong URL is not automatically evidence that SSE is available.
Connect from Python
The Python SDK uses an asynchronous context manager for lifecycle management. Entering the context connects; leaving it disconnects cleanly.
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from mcp.client.stdio import stdio_client
server = StdioServerParameters(
command="node",
args=["/absolute/path/to/server.js"],
)
async with stdio_client(server) as (read_stream, write_stream):
async with ClientSession(read_stream, write_stream) as session:
await session.initialize()
tools = await session.list_tools()
print(tools)For a remote server, use the Python SDK’s HTTP transport documented for your installed version and retain the same lifecycle rule: initialize inside the context and close it when finished. Do not mix TypeScript transport classes with Python APIs.
Complete the handshake, then inspect capabilities
Connecting is not the same as successfully using a server. Wait for the connection call or context entry to finish before listing tools. The initialize handshake returns the negotiated protocol information, server capabilities, and instructions that the client should follow.
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- List tools before invoking one, and verify its input schema.
- Check whether the server exposes resources or prompts in addition to tools.
- Honor server instructions and capability flags; do not assume every MCP server implements every operation.
- Keep the client alive for the complete operation, then close it through the SDK’s lifecycle API.
Authentication for protected remote servers
A protected HTTP MCP endpoint can respond with 401 Unauthorized. In the documented authorization flow, that response signals the host to discover authorization metadata, obtain user consent through OAuth, acquire a token, and retry the request. Authorization may cover every request to a server or only selected protected tools.
Because discovery and client support vary, follow the server’s authorization metadata and your host’s OAuth instructions. A static configuration containing a copied bearer token is not a universal solution and can expose credentials.
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Troubleshoot the connection
spawn ... ENOENT
Cause: The executable configured for stdio cannot be found in the environment of the process launching the host. Fix: run the exact command from that environment, use an absolute executable path, correct the command name, and verify that the host has the expected PATH.
HTTP endpoint will not connect
Cause: The URL is wrong, the server does not expose Streamable HTTP, or a proxy is blocking the request. Fix: copy the endpoint exactly, confirm the server’s advertised transport, and use the documented SSE fallback only if the server is SSE-only.
HTTP 401 or authorization denied
Cause: The endpoint is protected and the host has not completed its authorization flow, or the token lacks permission for the requested operation. Fix: check the server’s authorization discovery response and confirm that your MCP host supports the required OAuth steps.
Connection succeeds but no tools appear
Cause: The server may expose resources or prompts instead of tools, or the client queried before initialization completed. Fix: await initialization, inspect all capability fields, and use the operation supported by that server.
Protocol or revision mismatch
Cause: SDK and server releases evolve. Fix: use compatible SDK documentation, avoid hard-coding optional advanced revision negotiation, and let the SDK’s default compatibility behavior operate unless your project specifically requires a newer revision.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Reliability and lifecycle practices
- Use absolute local paths and pin the runtime environment used by the host.
- Log the selected transport, endpoint (without secrets), initialization result, and shutdown errors.
- Reconnect with a new client after a failed transport attempt, especially when switching from Streamable HTTP to SSE.
- Close local clients so child processes terminate, and close HTTP clients so sessions are released. If an HTTP server issued a session ID, follow the SDK’s documented termination behavior.
- Keep credentials outside source control and avoid logging authorization headers.
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FAQ
Can I connect to any MCP server with one configuration format?
No. The transport, executable arguments, endpoint, authentication, and host configuration surface depend on the server and MCP client. Use the server’s documented transport rather than assuming a universal file path or button.
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Use Streamable HTTP when available. SSE is a legacy compatibility path for servers that do not support Streamable HTTP and clients that still implement it.
What does a successful MCP connection provide?
After initialization, the client has the negotiated protocol information, server instructions, and capability information needed to discover supported tools, resources, or prompts.
Frequently Asked Questions
Can I connect to any MCP server with one configuration format?
No. Transport, executable arguments, endpoint, authentication, and host configuration vary by server and client.
Should a new remote server use SSE?
Prefer Streamable HTTP. SSE is for legacy compatibility when the server lacks Streamable HTTP support.
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What does a successful MCP connection provide?
The initialization handshake returns negotiated protocol information, instructions, and capabilities for supported operations.
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