A Spring Boot Kotlin MCP bridge that exposes backend tools to Flowise-style agents over Server-Sent Events. Tools register through provider interfaces, and the agent connects to an SSE endpoint.
The problem
Agent builders often start on a visual workflow canvas before they have a clean boundary for tools. Flowise and LangChain-compatible runtimes can call external tools, but that leaves open where the tool contract lives, how it is discovered, and how the bridge stays understandable as the agent grows.
sse-mcp-server exposes an MCP-style server over SSE, so an agent can discover and call backend tools without coupling each one to the workflow canvas.
Architecture
The server is a Spring Boot Kotlin application with a configurable MCP server. It has:
- an SSE endpoint for agents to connect to
- a message endpoint for tool execution
- a manifest endpoint for automatic tool discovery
- provider-based tool registration so tools can be added without changing the transport
- Docker Compose support for running locally with Flowise
The initial tools are arithmetic and date/time operations, which keeps the example about the integration.
Trade-offs
This is a small bridge you can read through, with no orchestration of its own. It fits when you need to connect an agent runtime to a controlled set of backend tools.
I chose SSE because it is easy to reason about from a browser-era stack, suits long-lived agent connections, and is simple to debug locally. Richer two-way interaction has to go through the message endpoints or a different transport.
Details
- Repository: github.com/yonatankarp/sse-mcp-server
- Stack: Kotlin, Spring Boot, Server-Sent Events, MCP-style tool discovery, Docker Compose
- Built-in example tools: math and date/time providers