Bug or something I'm doing wrong ?

[dacr]

Consider this scala script :

//> using scala 3.7.1
//> using dep org.slf4j:slf4j-api:2.0.17
//> using dep org.slf4j:slf4j-simple:2.0.17
//> using dep com.tjclp::fast-mcp-scala:0.1.1
//> using options "-Xcheck-macros" "-experimental"

import com.tjclp.fastmcp.core.*
import com.tjclp.fastmcp.macros.RegistrationMacro.*
import com.tjclp.fastmcp.server.{FastMcpServer, FastMcpServerSettings}
import zio.*

// Define annotated tools, prompts, and resources
object Example {
  @Tool(name = Some("hello"), description = Some("Say hello"))
  def hello(): String = "Hello, world!"
}

object ExampleServer extends ZIOAppDefault {
  override def run = {
    val settings = FastMcpServerSettings(
      debug=true,
      logLevel="DEBUG",
    )
    for {
      server  <- ZIO.succeed(FastMcpServer(name = "hello-mcp-server", settings = settings))
      _       <- ZIO.attempt(server.scanAnnotations[Example.type])
      _       <- ZIO.log("Starting stdio server...")
      _       <- server
        .runStdio()
        .tapError(error => ZIO.log(s"Error running stdio: $error"))
        .onInterrupt(ZIO.log("Server interrupted"))

    } yield ()
  }
}

ExampleServer.main(args)

Nothing happens when I try to invoke the hello tool :

scala-cli hello-mcp-server.sc
Compiling project (Scala 3.7.1, JVM (21))
Compiled project (Scala 3.7.1, JVM (21))
[ToolProcessor] registering tool: hello
timestamp=2025-07-18T12:54:49.559990339Z level=INFO thread=#zio-fiber-1418526459 message="Starting stdio server..." location=<empty>.hello$minusmcp$minusserver$_.ExampleServer.run file=hello-mcp-server.scala line=48
[FastMCPScala] Registering 1 tools with the MCP server:
[FastMCPScala] - Registering Tool: hello
[FastMCPScala] Processing 0 resource definitions for Java server registration...
[FastMCPScala] Registering 0 prompts...
[FastMCPScala] MCP Server 'hello-mcp-server' configured.
[FastMCPScala] 'hello-mcp-server' running on stdio – press Ctrl-C to stop.
{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion": "2024-11-05"}}
[pool-1-thread-1] INFO io.modelcontextprotocol.server.McpAsyncServer - Client initialize request - Protocol: 2024-11-05, Capabilities: null, Info: null
{"jsonrpc":"2.0","id":0,"result":{"protocolVersion":"2024-11-05","capabilities":{"experimental":{},"logging":{},"tools":{"listChanged":true}},"serverInfo":{"name":"hello-mcp-server","version":"0.1.0"}}}
{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hello"}}

Any idea ?

[dacr]

ok I've made another try using directly the java sdk, and I got the same behavior, I tried with such script, and ask for tools list :

//> using scala 3.7.1
//> using dep org.slf4j:slf4j-api:2.0.17
//> using dep org.slf4j:slf4j-simple:2.0.17
//> using dep io.modelcontextprotocol.sdk:mcp:0.10.0

import io.modelcontextprotocol.server.McpServer
import io.modelcontextprotocol.server.transport.StdioServerTransportProvider
import io.modelcontextprotocol.spec.McpSchema.ServerCapabilities
import io.modelcontextprotocol.spec.McpServerTransportProvider

/*
{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion": "2024-11-05"}}
{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}
*/

object ExampleServer {
  def main(args: Array[String]): Unit = {
    val transportProvider = StdioServerTransportProvider()
    val capabilities = ServerCapabilities
      .builder()
      .resources(false, true)
      .tools(true)
      .prompts(true)
      .logging()
      .build()
    val helloServer =
      McpServer
        .sync(transportProvider)
        .serverInfo("hello-server", "1.0.0")
        .capabilities(capabilities)
        .build()

    Thread.sleep(60000)
    helloServer.close()
  }
}

ExampleServer.main(args)

[arcaputo3]

I was able to get this working with running the MCP inspector via npx @modelcontextprotocol/inspector scala-cli <full_path>/server.sc. Can you please verify this works for you?