To integrate an MCP client, connect your host application to an MCP server with an SDK, choose a transport the server supports, complete the initialization handshake, then call only the tools, resources, and prompts advertised in the negotiated capabilities. Use stdio for a local child process, Streamable HTTP for an HTTP endpoint, and legacy HTTP+SSE only when the server does not support Streamable HTTP. The right design also depends on where the server runs, how credentials are supplied, which protocol versions can be negotiated, and what user approval is required.
MCP is an open standard for connecting AI applications to external systems, including data sources, tools, and workflows, as described in the official MCP overview.
What an MCP client integration does
An MCP host is the application the user interacts with: an AI assistant, agent, IDE, or your own service. The host creates an MCP client, and that client maintains a JSON-RPC connection to an MCP server. The server exposes capabilities such as tools, resources, and prompts.
Connection is more than opening a socket. During initialization, client and server exchange protocol information and capabilities. After the handshake, your code should discover what the server actually declared and avoid sending operations it did not advertise. A server may support tools but not resources, or may expose optional features such as roots, sampling, or elicitation.
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Keep three versions separate:
- SDK package version: the version installed in your application.
- Protocol version: the MCP revision negotiated for a particular connection.
- Server implementation version: the release of the remote or local server.
A newer SDK does not force every connection to use the newest protocol revision. The OpenAI Agents SDK documentation describes discovery with fallback to the legacy initialize handshake when a server does not support the probe; compatible clients can therefore interoperate with older servers.
Choose the transport and deployment pattern
| Pattern | Use it when | Important operational point |
|---|---|---|
| Streamable HTTP | The server is reachable at an HTTP endpoint, locally or remotely. | The TypeScript SDK creates a StreamableHTTPClientTransport; OpenAI documents it for remote MCP servers. |
| stdio | Your application can launch a local MCP server process. | The client speaks JSON-RPC over the child process’s standard input and output. You own process startup, logs, limits, and shutdown. |
| HTTP+SSE | The server offers only the older SSE transport. | Try Streamable HTTP first. If it is unsupported, create a fresh client and retry with SSE. |
| In-memory linked transport | Client and server run in one process, especially in tests. | No network or child process is needed, which makes deterministic integration tests easier. |
| Hosted MCP handling | Your model/API provider should connect to a public MCP server. | The provider performs discovery and calls on the model’s behalf; verify supported models and approval behavior. |
| Private-server tunnel | A local, on-premises, or firewalled server must remain unexposed. | Use a supported secure tunnel rather than publishing the server directly. |
The transport must match what the server implements. A server URL alone does not prove that it accepts Streamable HTTP, and an SSE-only server cannot be made Streamable HTTP-compatible by changing the client URL.
Prepare an integration safely
Confirm the server contract
- Record the endpoint or executable command, supported transports, authentication method, and expected protocol range.
- Identify which tools can mutate data, send messages, delete records, or spend money.
- Read the server’s instructions and document required environment variables, working directory, and timeouts.
Install the SDK line that matches your runtime
The TypeScript SDK v2 overview identifies v2 as its stable release line and says it implements the 2026-07-28 MCP specification. The Java SDK client documentation provides synchronous and asynchronous APIs plus stdio, SSE, and Streamable HTTP transports. Check each SDK’s current package, runtime requirements, migration notes, and authentication hooks before copying an example.
Decide what the user must approve
MCP servers can receive model context and act with supplied credentials. Use a trusted, preferably official server when one exists, provide least-privilege credentials, and require approval before sensitive tool calls. Keep access tokens in authorization headers or SDK authorization fields, not in URLs. OpenAI’s MCP server guidance describes approval controls for Responses API integrations; the exact default depends on the product and configuration you use.
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Connect a local server over stdio in TypeScript
Use stdio when your host can start the server as a child process. The following example uses the TypeScript SDK, lists the tools after the handshake, and closes the process cleanly.
- Install Node.js and the SDK:
npm install @modelcontextprotocol/sdk. - Replace
server.jswith the executable and arguments for your server. - Run the client and inspect the returned tool definitions before enabling model access.
import { Client } from '@modelcontextprotocol/sdk/client/index.js';
import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
const client = new Client({ name: 'example-host', version: '1.0.0' });
const transport = new StdioClientTransport({
command: 'node',
args: ['server.js']
});
try {
await client.connect(transport); // initialization and capability negotiation
const result = await client.listTools();
console.log(JSON.stringify(result.tools, null, 2));
} finally {
await transport.close();
}The server process must write protocol messages to stdout only. Send diagnostic logging to stderr so it does not corrupt JSON-RPC traffic. In production, bound the child process lifetime, capture stderr, redact secrets from logs, and close the transport during application shutdown.
Connect a remote server with Streamable HTTP
For an HTTP endpoint, construct a Streamable HTTP transport and connect the same client. Authentication options differ by SDK and server, so follow the selected SDK’s transport and authorization documentation rather than placing a token in the URL.
import { Client } from '@modelcontextprotocol/sdk/client/index.js';
import { StreamableHTTPClientTransport } from '@modelcontextprotocol/sdk/client/streamableHttp.js';
const client = new Client({ name: 'remote-host', version: '1.0.0' });
const transport = new StreamableHTTPClientTransport(
new URL('https://mcp.example.com/mcp')
);
try {
await client.connect(transport);
const tools = await client.listTools();
console.log(`Discovered ${tools.tools.length} tools`);
} finally {
await transport.close();
}After connect() completes, retain the negotiated session while you perform discovery and calls. Close the HTTP session when the host exits or the user disconnects. If the endpoint returns an authentication challenge, configure the SDK’s supported authorization mechanism and retry; do not silently downgrade to an unauthenticated connection.
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Handle an SSE-only server
SSE is a compatibility path for older servers. The TypeScript client guide recommends trying Streamable HTTP first and, when that fails because the server is SSE-only, retrying with a new client and an SSE transport. Do not reuse a partially initialized client or transport for the fallback. Confirm that the server really advertises SSE before treating a network error as a transport mismatch.
Use negotiated capabilities correctly
The initialization response contains protocol information, server capabilities, and server instructions. Build your feature gates from that response:
- Call tool-listing and tool-execution methods only when the server declares tool support.
- Request resources or prompts only when those capabilities are present.
- Honor server instructions as integration input, while still applying your host’s policy and approval rules.
- If your client offers roots, sampling, or elicitation, advertise and implement only the features your host can safely handle.
Capability negotiation is a contract, not a promise that every MCP server supports every operation. Test both the capability-present and capability-absent paths.
Compare SDK choices beyond TypeScript
Choose the SDK that fits the host language and its operational model:
- TypeScript: the v2 client guide covers
Client, stdio, Streamable HTTP, SSE fallback, in-memory linked transports, and orderly shutdown. It is a natural choice for Node-based hosts and IDE integrations. - Java: the official client supports synchronous and asynchronous APIs, protocol and capability negotiation, tool discovery and execution, resources, prompts, and optional roots, sampling, and elicitation. Its core module documents stdio, SSE, and Streamable HTTP.
- Python or another language: verify the SDK’s current transport coverage, async model, authentication integration, and migration notes. Do not infer feature parity from package names alone.
Package release numbers and protocol revisions are independent. Pin and update packages deliberately, then test connections against every server version you support.
Hosted and private deployments
Provider-hosted connections
A hosted MCP tool path lets a supported API provider discover and call a public server for the model. This can remove client-side transport code, but you still own server trust, data review, tool approvals, and error handling. Read the provider’s current MCP documentation for supported models and logging behavior.
Private servers and tunnels
For an on-premises or firewalled server, use a supported private MCP tunnel. OpenAI documents Secure MCP Tunnel for supported products. The tunnel keeps the server from being publicly exposed, but it does not remove the need for authentication, least-privilege credentials, or user approval.
Cloud hosting
If you need a remote endpoint, Google Cloud documents a Cloud Run deployment path in its Host MCP servers on Cloud Run guide. Confirm current MCP support, pricing, region availability, authentication, and commercial terms before selecting a provider.
Security controls that belong in the client
- Trust: connect only to servers whose owner and code you can evaluate; prefer an official service-hosted server when available.
- Credential scope: issue separate, least-privilege credentials for each server and environment.
- Data minimization: send only the context required for the requested operation and review what server-defined tools can request.
- Approval: pause for explicit approval before destructive, financial, external-communication, or permission-changing actions.
- Secret handling: use headers or authorization fields, secret managers, and redacted logs; never put bearer tokens in query strings.
- Isolation: sandbox local child processes and restrict filesystem, network, and environment access where practical.
Reliability and performance in production
stdio performance is usually dominated by process startup, while remote transports add connection setup, network latency, authentication, and server work. Keep a healthy remote session for a burst of related operations instead of reconnecting for every tool call, but implement idle cleanup and reconnect logic for expired sessions.
Set explicit connect, tool-call, and shutdown timeouts. Bound tool arguments and result sizes, stream or paginate large data where the server supports it, and record request IDs, negotiated protocol version, transport, latency, and failure category without logging secrets or sensitive payloads.
Test these cases before rollout:
- server unavailable, DNS failure, TLS failure, and authentication rejection;
- server supports an older protocol revision;
- capability is absent or a tool disappears after discovery;
- malformed results, oversized results, and tool execution errors;
- child-process crash, stdout contamination, and graceful shutdown;
- approval denied, cancelled, or timed out.
Troubleshooting common integration failures
| Symptom | Likely cause | Fix |
|---|---|---|
| JSON parse errors over stdio | The server wrote logs or a banner to stdout. | Move diagnostics to stderr and ensure only JSON-RPC messages use stdout. |
| HTTP connection succeeds but initialization fails | Wrong endpoint path, unsupported transport, or missing authentication. | Verify the server’s documented MCP endpoint and transport, then configure authorization through the SDK. |
| Tool list is empty | The server does not advertise tools, or discovery occurred before initialization completed. | Wait for connect() to finish and inspect negotiated capabilities and server instructions. |
| SSE fallback also fails | The server is not actually SSE-only, or the fallback reused a stale client. | Create a fresh client and transport, confirm the server’s transport documentation, and check proxy support for event streams. |
| Works locally but not in production | Different runtime, environment variables, network policy, or credential scope. | Compare the executable path, working directory, outbound access, secret injection, and protocol logs in both environments. |
| Calls hang during shutdown | Open sessions or child processes were not closed. | Close the transport in a finally block and register application shutdown handlers. |
| Older server rejects a new client | Protocol discovery or feature assumptions are incompatible. | Use the SDK’s documented legacy-initialize fallback, limit requests to declared capabilities, and test the server’s supported protocol range. |
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FAQ
Does every MCP client need to implement every capability?
No. A client should advertise only features it supports and invoke only operations declared by the connected server. Optional capabilities are negotiated per connection.
Can I keep an MCP server private without hosting it publicly?
Yes. Use local stdio when the host can launch the server, or a supported private-server tunnel when the server remains inside a private network.
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Is an SDK upgrade the same as a protocol upgrade?
No. The SDK package and negotiated MCP protocol are separate. A current SDK may connect using an older protocol revision when compatibility permits.
When should I choose SSE?
Use SSE as a compatibility fallback only when the server documents HTTP+SSE and does not accept Streamable HTTP.
Frequently Asked Questions
What should I log for an MCP connection without exposing secrets?
Log the transport, endpoint name, negotiated protocol version, capability summary, request identifier, duration, and error category; redact tokens, arguments, and sensitive results.
Should a client reconnect automatically after a dropped session?
It can, provided reconnection is bounded, authentication is repeated safely, initialization and capability discovery run again, and in-flight side-effecting calls are not duplicated without an idempotency strategy.
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