@pumped-fn/sdk-mcp

Status: experimental. APIs change without notice; not recommended for production yet.

Expose pumped-fn flows — including your @pumped-fn/sdk agent tools — as an MCP server. Each tool call runs the flow inside your scope — same deps, presets, and trace as any other graph edge.

A flow becomes a tool by carrying an mcpToolMeta tag (description + Zod input shape). List the flows in mcpConfig; the mcpServer resource registers each and stays generic. The input shape is declared once and shared between the flow's parse and the tool schema.

import { atom, createScope, flow } from "@pumped-fn/lite"
import { mcpConfig, mcpServer, mcpToolMeta } from "@pumped-fn/sdk-mcp"
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"
import { z } from "zod"

const rate = atom({ factory: () => 1.1 })

const amount = { amount: z.number() }

const convert = flow({
  name: "convert",
  parse: (raw) => z.object(amount).parse(raw),
  deps: { rate },
  tags: mcpToolMeta({ description: "Convert an amount", inputSchema: amount }),
  factory: (ctx, { rate }) => ({ converted: ctx.input.amount * rate }),
})

const scope = createScope({
  tags: mcpConfig({ name: "billing", version: "1.0.0", tools: [convert] }),
})
const ctx = scope.createContext()

// The composition root owns the transport, exactly as it owns the scope.
const server = await ctx.resolve(mcpServer)
await server.connect(new StdioServerTransport())

The MCP SDK validates arguments against each flow's inputSchema, then the handler execs the flow with the validated value as raw input. A flow's own parse runs after MCP validation, so its input must match the schema's output. A thrown error's message becomes the isError result text sent to the client, so throw client-safe messages. Cleanup closes the server and drains in-flight calls; for a clean shutdown, close the client before disposing the scope. For tests, connect an InMemoryTransport.createLinkedPair() instead of stdio.

Part of pumped-fn — start with the docs or the mental model.