Add MCP Tool

Adding a New MCP Tool

Follow these steps in order when adding a new MCP tool to the server.

Step 1: Create Request DTO (if tool has parameters)

Create a new class in src/main/java/com/ohmydigital/mcpluceneserver/mcp/dto/.

Pattern:

public record MyToolRequest(
    @Description("Description of the parameter")
    String requiredParam,
    @Nullable @Description("Optional parameter")
    String optionalParam
) {
    public static MyToolRequest fromMap(final Map<String, Object> map) {
        return new MyToolRequest(
            (String) map.get("requiredParam"),
            (String) map.get("optionalParam")
        );
    }
}

• Use @Description annotation for MCP schema generation
• Use @Nullable for optional fields
• Always provide a fromMap() static factory method

Step 2: Create Response DTO

Create in the same mcp/dto/ directory.

Pattern:

public record MyToolResponse(
    boolean success,
    @Nullable String error,
    // ... data fields
) {
    public static MyToolResponse success(/* data params */) {
        return new MyToolResponse(true, null, /* data */);
    }

    public static MyToolResponse error(final String message) {
        return new MyToolResponse(false, message, /* nulls */);
    }
}

All responses MUST include success (boolean) and error (nullable String).

Step 3: Register Tool Specification

In LuceneSearchTools.getToolSpecifications(), add a new ToolSpecification:

new ToolSpecification("myToolName", "Human-readable description", schemaJson)

• Tool name: camelCase
• Description: concise, explains what it does and when to use it
• Schema: JSON Schema for the request parameters

Step 4: Implement Handler

Add a handler method in LuceneSearchTools:

private CallToolResult myToolName(final Map<String, Object> arguments) {
    try {
        final var request = MyToolRequest.fromMap(arguments);
        // ... implementation
        final var response = MyToolResponse.success(/* data */);
        return new CallToolResult(List.of(new TextContent(objectMapper.writeValueAsString(response))));
    } catch (final SpecificException e) {
        logger.error("myToolName failed", e);
        return new CallToolResult(List.of(new TextContent(
            objectMapper.writeValueAsString(MyToolResponse.error(e.getMessage())))));
    }
}

Wire the handler in the callTool() method's switch/if-else chain.

Step 5: Update README.md

MANDATORY - Add tool documentation to README.md:

• Tool name, description, parameters
• Example request/response
• Add to the tools overview table

Step 6: Test

1. Write unit tests for the DTO fromMap() methods
2. Write integration tests if the tool interacts with the index
3. Test with Claude Desktop manually

Reference Examples

Look at these existing tools for patterns:

• Simple query tool: search() in LuceneSearchTools.java
• Admin operation (async): optimizeIndex() in LuceneSearchTools.java
• Configuration tool: setCrawlerDirectories() in LuceneSearchTools.java

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