---
applyTo: '**/*.java, **/application*.properties, **/application*.yml, **/application*.yaml'
description: 'Quarkus MCP Server development standards and instructions, with Streamable HTTP (preferred) and legacy HTTP SSE transports'
---
# Quarkus MCP Server

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

```bash
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)


---
Source: awesome-copilot (github/awesome-copilot) https://github.com/github/awesome-copilot/blob/cb64ad12e32737ae764becd6885462e9b4c7cb00/instructions/quarkus-mcp-server-sse.instructions.md
MIT License

Copyright GitHub, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.