The Model Context Protocol (MCP) includes support for tools, allowing AI models to a) Get metadata (descriptions) of tool input and output; b) Provide input, call/take action and c) get output via the use of one or more of the available tools
Currently, the specification provides no way to communicate tool groupings and mcp metadata between mcp servers and clients. Tool grouping, however, will become important as the number, variety and function of tools increases on a given MCP server/servers, along with the need for orchestration of multiple tools (sequencing the input and output of multiple tools to accomplish a given task) becomes more common. There are also lots of use cases for dynamic group creation for organization, testing, and model red teaming.
I've started a discussion on a proposal for enhancing the mcp specification to support ToolGroups. The code examples below are based upon this schema addition from this comment forward, and with the associated additions to the mcp-java-sdk, and the mcp-annotations project.
For example, in the com.composent.ai.mcp.examples.toolgroup.api project is the declaration of an ExampleToolGroup interface class, with McpTool and McpToolGroup metadata:
@McpToolGroup(description="Arithmetic operations exposed as mcp tools")
public interface ExampleToolGroup {
@McpTool(description = "computes the sum of the two double precision input arguments a and b")
double add(@McpToolParam(description = "x is the first argument") double x,
@McpToolParam(description = "y is the second argument") double y);
@McpTool(description = "return the product of the two given double precision arguments named a and b")
double multiply(@McpToolParam(description = "x is the first argument") double x,
@McpToolParam(description = "y is the second argument") double y);
@McpTool(description = "return asynchronously the sum of the two double precision input arguments a and b")
Mono<Double> asyncAdd(@McpToolParam(description = "x is the first argument") double x,
@McpToolParam(description = "y is the second argument") double y);
@McpTool(description = "return asynchronously the product of the two given double precision arguments named a and b")
Mono<Double> asyncMultiply(@McpToolParam(description = "x is the first argument") double x,
@McpToolParam(description = "y is the second argument") double y);
}Each method in the interface is annotated with the @McpTool and @McpToolParam annotations from the mcp-annotations project. There are both sync methods (add, multiply) and async methods (asyncAdd and asyncMultiply).
From the com.composent.ai.mcp.examples.toolgroup.mcpserver project, here is the full implementation of the above interface.
Here is the OSGi component that implements the ExampleToolGroup interface.
@Component(immediate = true)
public class ToolGroupComponent implements ExampleToolGroup {
private static Logger logger = LoggerFactory.getLogger(ToolGroupComponent.class);
@Reference
private SyncMcpToolGroupServer syncServer;
@Reference
private AsyncMcpToolGroupServer asyncServer;
// Instance created in activate
private List<SyncToolSpecification> syncSpecifications;
private List<AsyncToolSpecification> asyncSpecifications;
@Activate
void activate() {
// Add to syncServer
syncSpecifications = syncServer
.addToolGroups(this, ExampleToolGroup.class);
// Add to asyncServer
asyncSpecifications = asyncServer
.addToolGroups(this, ExampleToolGroup.class);
}
@Deactivate
void deactivate() {
if (syncSpecifications != null) {
this.syncServer.removeTools(syncSpecifications);
syncSpecifications = null;
}
if (asyncSpecifications != null) {
this.asyncServer.removeTools(asyncSpecifications);
asyncSpecifications = null;
}
}
@Override
public double add(double x, double y) {
logger.debug("Adding x={} y={}", x, y);
return x + y;
}
@Override
public double multiply(double x, double y) {
logger.debug("Multiplying x={} y={}", x, y);
return x * y;
}
@Override
public Mono<Double> asyncAdd(double x, double y) {
logger.debug("Async Adding x={} y={}", x, y);
return Mono.just(add(x, y));
}
@Override
public Mono<Double> asyncMultiply(double x, double y) {
logger.debug("Async Multiplying x={} y={}", x, y);
return Mono.just(multiply(x, y));
}
}The McpServer tool specification for the ExampleToolGroup is created on component activation here:
syncSpecifications = syncServer.addToolGroups(this, ExampleToolGroup.class);The SyncMcpToolGroupProvider class (syncServer type) is from this package.
When the syncServer is injected into the ToolGroupComponent, and it is activated, the tool groups and the sync tools discovered on the ExampleToolGroup interface are added to the syncServer via addToolGroups.
As appropriate for the timing/lifecycle of these components, the toolspecs can also be dynamically removed from the syncServer:
if (syncSpecifications != null) {
this.syncServer.removeTools(syncSpecifications);
syncSpecifications = null;
}Once these specifications are added to a server, MCP clients are able to list the tools, use the toolgroup and tool descriptions to decide on tools to call, provide required input to those calls, make the actual call to the tool(s) and receive output . Note that the ExampleTools has both sync and async tool methods, and the McpSyncServer and McpSyncServer get the appropriate types of tools from the ExampleTools interface class through reflection on the ExampleToolGroup.class.
Note that the use of Java interfaces in this way automatically adds MCP metadata (descriptions from the @McpTool and @McpToolParam) to the api contract. This can be easily duplicated in other languages...e.g. Python, C++, or Typescript via decorators, annotations, and abstract classes. Nested ToolGroups can also be created/added (on the mcp server) in other ways...e.g. via db access, filesystem, other tooling, or via developer or user input.