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Quarkus Mcp Server Sse

Quarkus MCP Server development standards and instructions, with Streamable HTTP (preferred) and legacy HTTP SSE transports

Install

Apply these instructions only when the project uses a Quarkus MCP Server extension (mcp-server-http, or the legacy mcp-server-sse).

Build MCP servers with Java 21, Quarkus, and Streamable HTTP transport (legacy HTTP SSE is also supported).

Stack

  • Java 21 with Quarkus Framework
  • MCP Server Extension: mcp-server-http (io.quarkiverse.mcp:quarkus-mcp-server-http), which serves both transports: legacy HTTP/SSE at http://localhost:8080/mcp/sse and Streamable HTTP (preferred; SSE is deprecated in the MCP spec) at http://localhost:8080/mcp
  • mcp-server-sse is not managed by recent Quarkus platform BOMs (verified: absent from 3.40.1); the Quarkus CLI silently falls back to an older platform stream when asked for it. Use it only to keep an existing project that already depends on it.
  • CDI for dependency injection

Quick Start

quarkus create app --no-code -x rest-client-jackson,qute,mcp-server-http your-domain-mcp-server

Structure

  • Use standard Java naming conventions (PascalCase classes, camelCase methods)
  • Organize in packages: model, repository, service, mcp
  • Use Record types for immutable data models
  • State management for immutable data must be managed by repository layer
  • Add Javadoc for public methods

MCP Tools

  • Must be public methods in @ApplicationScoped CDI beans
  • Use @Tool(name="tool_name", description="clear description")
  • Never return null - return error messages instead
  • Always validate parameters and handle errors gracefully

Architecture

  • Separate concerns: MCP tools → Service layer → Repository
  • Use constructor injection (@Inject is optional on a single constructor)
  • Make data operations thread-safe
  • Use Optional<T> to avoid null pointer exceptions

Common Issues

  • Don't put business logic in MCP tools (use service layer)
  • For expected business errors throw io.quarkiverse.mcp.server.ToolCallException (its message becomes a failed tool result); don't let other unhandled exceptions escape, as they are reported as generic internal errors
  • Don't forget to validate input parameters
  • Test with edge cases (null, empty inputs)