@particle-academy/fancy-flow-mcp-js

MCP server that lets an agent author fancy-flow workflows headlessly on a TypeScript host — the Node twin of fancy-flow-mcp (Laravel).

Same 15 tools, same names, same arguments. An agent that learned to build graphs against the PHP server drives this one without relearning anything — and that claim is asserted by a test that reads the PHP source, not maintained by hand.

npx @particle-academy/fancy-flow-mcp-js

The split it is built around

We own whether a graph is well-formed; the host owns whether it is allowed to run.

Every issue crosses the wire tagged with which of those refused it:

{ "source": "schema", "level": "error",   "message": "message: Message is required", "nodeId": "log-1" }
{ "source": "host",   "level": "error",   "message": "This host cannot resume a paused run.", "nodeId": "ask-1" }

Those have different remedies — one is fixed by editing the graph, the other by granting a capability or picking another kind. Collapsing them costs an author real time chasing the wrong fix, so they are never merged.

Related MCP server: Orchestration MCP

Two entry points

The core was written first and deliberately depends on nothing, so a host that only wants to build and validate graphs never pays for a server it will not use.

No third-party runtime code, and no React. The server is agent-integrations' first-party MicroMcpServer, imported from its headless /mcp subpath, which imports no package at all. (Until 0.2.0 it was @modelcontextprotocol/sdk — see the changelog for what changed and what did not.)

Use it from a host

import { createFlowServer, MemoryDraftStore } from "@particle-academy/fancy-flow-mcp-js";
import { attachStdio } from "@particle-academy/agent-integrations/mcp/stdio";

const server = createFlowServer({
  store: new MemoryDraftStore(),

  // Your answer to "may I run this kind here?". Return a string to REFUSE —
  // and name the missing capability, because a refusal an author can act on is
  // worth more than a correct one they cannot.
  admits: (kind) =>
    kind.name.includes("terminal") ? "This host has no terminal sessions." : null,
});

attachStdio(server); // stdin/stdout; log to stderr, never stdout

Importing @particle-academy/agent-integrations yourself? Declare it in your own dependencies (>=0.45 <2.0) rather than relying on this package to bring it.

There is no need to call registerBuiltinKinds(): the kind registry fills itself on first read. It is also the wrong import for a headless host — @particle-academy/fancy-flow/registry pulls in React.

createFlowServer returns a transport-agnostic server. For anything other than stdio, attach any agent-integrations transport, or implement its two-member Transport (send, optional close) and hand each incoming frame to server.receive(transport, frame).

MemoryDraftStore is a convenience. Implement DraftStore (list / get / save / remove, sync or async) against your own storage and drafts survive a restart — this package never persists anything itself.

The tools

list_node_kinds reads the live registry, so kinds a host registered itself and kinds vendored from the marketplace are included. It is not a fixed list.

configure_node writes a config that fails validation and reports warnings rather than refusing. A half-configured node is a normal intermediate state when an agent builds a graph one step at a time; validate_workflow is the place that says "not finished".

run_workflow — read this before relying on it

It is a smoke test of wiring and routing, not a production run.

It takes no executor argument, and the executor registry is bound as a literal at the call site — the same shape the PHP twin uses. An agent-reachable run is structurally incapable of being pointed at your real infrastructure. Unrepresentable beats forbidden: a policy can be relaxed by a later edit; an absent parameter cannot be passed.

Two honest limits:

1. 9 of 31 builtin kinds have a TypeScript executor. The PHP twin's Builtin::executors() covers every kind; the TS runtime has no equivalent yet. The other 22 return ok: false with "No executor registered" — a true answer about this runtime, delivered as a result rather than an error. A test pins the count so the day it improves, this paragraph is forced to change.

2. Kind-level executors still apply. A host process that has called registerTerminalHost or registerLlmClient makes those reachable from here. That is your doing, not this package's, and it is said plainly rather than papered over.

Protocol revision

Speaks 2025-11-25, negotiating back to 2024-11-05 — the same family laravel/mcp speaks, which is what the PHP twin is built on, and what Claude Code and Codex speak. initialize echoes any of those a client asks for and answers 2025-11-25 otherwise.

It does not speak 2026-07-28, the revision that removed initialize and made the protocol stateless. Neither does the PHP twin. If you need to be reached by a 2026-07-28-only client, that gap is open and belongs to both twins together — a Node server that jumped ahead alone would stop being a twin.

Licence

MIT