A high‑level, developer‑friendly Scala 3 library for building Model Context Protocol (MCP) servers.
Features
- ZIO‑based effect handling and async support
- Annotation‑driven API (
@Tool,@Resource,@Prompt) - Automatic JSON Schema & handler generation via Scala 3 macros
- Seamless integration with the Java MCP SDK
Add to your build.sbt (defaulting to Scala 3.6.4):
libraryDependencies += "com.tjclp" %% "fast-mcp-scala" % "0.1.1"//> using scala 3.6.4
//> using dep com.tjclp::fast-mcp-scala:0.1.1
//> using options "-Xcheck-macros" "-experimental"
import com.tjclp.fastmcp.core.{Tool, ToolParam, Prompt, PromptParam, Resource}
import com.tjclp.fastmcp.server.FastMcpServer
import com.tjclp.fastmcp.macros.RegistrationMacro.*
import zio.*
// Define annotated tools, prompts, and resources
object Example:
@Tool(name = Some("add"), description = Some("Add two numbers"))
def add(
@ToolParam("First operand") a: Double,
@ToolParam("Second operand") b: Double
): Double = a + b
@Prompt(name = Some("greet"), description = Some("Generate a greeting message"))
def greet(@PromptParam("Name to greet") name: String): String =
s"Hello, $name!"
// Note: resource templates (templated URIs) are not yet supported;
// coming soon when the MCP java‑sdk adds template support.
@Resource(uri = "file://test", description = Some("Test resource"))
def test(): String = "This is a test"
object ExampleServer extends ZIOAppDefault:
override def run =
for
server <- ZIO.succeed(FastMcpServer("ExampleServer"))
_ <- ZIO.attempt(server.scanAnnotations[Example.type])
_ <- server.runStdio()
yield ()The above example can be run using scala-cli scripts/quickstart.scala from the repo root. You can run the server via the MCP inspector by running:
npx @modelcontextprotocol/inspector scala-cli <path_to_repo>/scripts/quickstart.scalaYou can also run examples directly from the command line:
scala-cli \
-e '//> using dep com.tjclp::fast-mcp-scala:0.1.1' \
--main-class com.tjclp.fastmcp.examples.AnnotatedServerIn Claude desktop, you can add the following to your claude_desktop_config.json:
{
"mcpServers": {
"example-fast-mcp-server": {
"command": "scala-cli",
"args": [
"-e",
"//> using dep com.tjclp::fast-mcp-scala:0.1.1",
"--main-class",
"com.tjclp.fastmcp.examples.AnnotatedServer"
]
}
}
}Note: FastMCP-Scala example servers are for demo purposes only and don't do anything useful
For additional examples and in‑depth docs, see docs/guide.md.
When hacking on FastMCP‑Scala itself, you can consume a local build in any project.
In your cloned repository, set a working version
ThisBuild / version := "0.1.1-SNAPSHOT"# From the fast-mcp-scala root
sbt publishLocalThen, in your consuming sbt project:
libraryDependencies += "com.tjclp" %% "fast-mcp-scala" % "0.1.1-SNAPSHOT"
publishLocalinstalls the artifact under~/.ivy2/local(or the Coursier cache when enabled).
# Package the library
sbt package
# Copy the JAR – adjust Scala version / name if you change them
cp target/scala-3.6.4/fast-mcp-scala_3-0.1.1-SNAPSHOT.jar \
/path/to/other-project/lib/Unmanaged JARs placed in a project's lib/ folder are picked up automatically by sbt.
You can use fast-mcp-scala in another scala‑cli project:
//> using scala 3.6.4
//> using dep com.tjclp::fast-mcp-scala:0.1.1
//> using options "-Xcheck-macros" "-experimental"You can also point directly at the local JAR:
//> using scala 3.6.4
//> using lib "/absolute/path/to/fast-mcp-scala_3-0.1.1.jar"
//> using options "-Xcheck-macros" "-experimental"