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Introduction

The MCP listener handles Model Context Protocol (MCP) client initialization requests automatically and enables a virtual asset to receive and respond to MCP messages sent over HTTP using Server-Sent Events (SSE). Connections from the client are kept open until the client closes the connection or an error occurs when sending MCP message to the client.

Requirements

MCP client that supports protocol version 2024-11-05 and communicates using HTTP with Server-Sent Events (SSE) transport.
This tool requires SOAtest/Virtualize 2024.1 or later, which needs to be configured to run with Java 17 or higher.

Installation

This tool can be installed from the UI or the command line.

UI Installation

Go to Parasoft > Preferences and click System Properties.
Click Add JARs and choose the com.parasoft.virtualize.listener.mcp-<version>.jar file.
Click Apply.
Restart SOAtest/Virtualize.

Command Line Installation

Add the com.parasoft.virtualize.listener.mcp-<version>.jar file to the system.properties.classpath property in your settings properties file. For example:

system.properties.classpath=<PATH_TO_JAR>/com.parasoft.virtualize.listener.mcp-<version>.jar

Usage

Once the MCP listener is installed, MCP Listener will be available in the Transports > Custom tab of the Virtual Asset configuration panel. Open this panel by double-clicking a virtual asset’s Virtualize Server node.

SOAtest and Virtualize 2025.2 > MCP Listener > select-mcp-listener.png

If multiple custom listeners are available, you can select the one you want to use from the Select Implementation menu.

Configuration

The following configuration options are available:

Connection Settings

Port	Specify the port for the listener. Value must be between `1` and `65535`. If empty, the listener will not start.
SSE Endpoint	Specify the SSE endpoint path. The default is `/sse`.
Worker Threads	Specify the number of worker threads used to process messages. `1` is the minimum value allowed. The default is `50`.
Heartbeat Interval	Specify a duration in seconds between sending heartbeat comments to MCP clients. Heartbeat comments are used to prevent connections from timing out. `1` is the minimum value allowed. The default is `15`.

Logging Settings

Log Level

Specify how much information you want logged to the console and the Event Monitoring view. The following levels are available:

1: error
2: warn
3: info
4: debug

The default is 2.

Configuring the Message Responders

While the MCP listener will return any response configured in the matching responder, it is recommended to format the response according to the JSON-RPC 2.0 specification for standard MCP communication.

Note that if the id field is provided in the response, it will be ignored and the id from the original request will be used instead. Additionally, if the jsonrpc field is not present in the response, it will be automatically added with the value 2.0.

Third-Party Content

This extension includes items that have been sourced from third parties as outlined below.

jackson-annotations (Apache License 2.0)
jackson-core (Apache License 2.0)
jackson-databind (Apache License 2.0)
MCP Java SDK (MIT License)
Reactor Core (Apache License 2.0)
Byte Buddy (Apache License 2.0)
Reactive Streams (MIT No Attribution)
SLF4J (MIT License)

Additional license details are available in this extension’s licenses folder.