mcp

Model Context Protocol, both directions. Call an MCP server’s tools, or be one.

MCP is JSON-RPC 2.0 with a fixed vocabulary: a handshake, then tools/*, resources/* and prompts/*.

Install

ecko get github.com/ecko-lang/mcp

Usage

MCP goes both directions: this package speaks to a server, and lets you be one.

Calling a server

import mcp

session = mcp.connect(mcp.stdio_transport("npx", ["-y", "@some/mcp-server"]))

for t in mcp.tools(session) {
    print("{t.name}: {t.description}")
}

print(mcp.text_of(mcp.call_tool(session, "search", { query: "ecko" })))
mcp.close(session)

Hand the tools straight to a model:

answer = ai "what changed in the changelog?" using mcp.as_tools(session)

Being a server

import mcp

mcp.serve_stdio([
    mcp.tool(
        "word_count",
        "Count the words in some text",
        { type: "object", properties: { text: { type: "string" } }, required: ["text"] },
        fn(args) len(split(trim(args.text), " ")),
    ),
], { name: "words", version: "1.0" })

Register it with a client by pointing it at ecko your_server.ecko.

Transports

stdio is how almost every MCP server ships: the client starts the process and uses the pipes it already has, so there is no port and nothing to authenticate. Needs exec.

mcp.stdio_transport("npx", ["-y", "@some/mcp-server"], { timeout_ms: 30000 })

HTTP is the shape a hosted server takes. Needs net.

token = secret(os.env("MCP_TOKEN"))
mcp.http_transport("https://mcp.example.com/", {
    headers: { Authorization: "Bearer {reveal(token)}" },
})

mcp.fake(handler) is a transport backed by a function, for tests. Needs no capability at all.

API

Client

Server