Transports

This page explains the transport mechanisms available for MCP communication.

Overview

The MCP specification currently defines two standard transports for client-server communication. The stdio transport starts an MCP server as a subprocess and communicates over standard in and out. The HTTP transports connects to a running HTTP server. The HTTP transport is defined in two variants: the "Streamable HTTP" variant (introduced in the protocol version 2025-03-26) replaces the "HTTP/SSE" transport (introduced in protocol version 2024-11-05). The "HTTP/SSE" transport is considered deprecated, but it’s still supported by most clients and servers.

This extension supports the stdio transport and both variants of the HTTP transport. Moreover, it also supports the unofficial websocket transport.

STDIO Transport

If you want to use the stdio transport you’ll need to add the io.quarkiverse.mcp:quarkus-mcp-server-stdio extension to your build file first. For instance, with Maven, add the following dependency to your POM file:

<dependency>
    <groupId>io.quarkiverse.mcp</groupId>
    <artifactId>quarkus-mcp-server-stdio</artifactId>
    <version>1.9.0</version>
</dependency>
If you use the stdio transport then your app should not write anything to the standard output. Quarkus console logging is automatically redirected to the standard error. And the standard output stream is set to "null" when the app is started by default.

See Getting Started with STDIO for a complete tutorial.

HTTP Transport

If you want to use the HTTP transport you’ll need to add the io.quarkiverse.mcp:quarkus-mcp-server-http extension to your build file first. For instance, with Maven, add the following dependency to your POM file:

<dependency>
    <groupId>io.quarkiverse.mcp</groupId>
    <artifactId>quarkus-mcp-server-http</artifactId>
    <version>1.9.0</version>
</dependency>
The artifactId has changed from quarkus-mcp-server-sse to quarkus-mcp-server-http in version 1.8.0. However, the old artifactId should still work because it’s relocated.

This artifact contains both versions of the HTTP transport. The MCP endpoint (as defined in 2025-03-26) is exposed at {rootPath}, i.e. /mcp by default. The SSE endpoint (as defined in 2024-11-05) is exposed at {rootPath}/sse, i.e. /mcp/sse by default. The {rootPath} is set to mcp by default, but it can be changed with the quarkus.mcp.server.sse.root-path configuration property.

The Resumability and Redelivery for the Streamable HTTP is not supported yet.

See Getting Started with HTTP for a complete tutorial.

WebSocket Transport

If you want to use the WebSocket transport you’ll need to add the io.quarkiverse.mcp:quarkus-mcp-server-websocket extension to your build file first. For instance, with Maven, add the following dependency to your POM file:

<dependency>
    <groupId>io.quarkiverse.mcp</groupId>
    <artifactId>quarkus-mcp-server-websocket</artifactId>
    <version>1.9.0</version>
</dependency>

The WebSocket endpoint is exposed at {endpointPath}. The {endpointPath} is set to /mcp/ws by default, but it can be changed with the quarkus.mcp.server.websocket.endpoint-path configuration property.

Using the BOM

You can also use the BOM (Bill Of Materials) to control the versions of all io.quarkiverse.mcp dependencies:

+

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>io.quarkiverse.mcp</groupId>
            <artifactId>quarkus-mcp-server-bom</artifactId>
            <version>1.9.0</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

See Also