enpilink

The open, account-free full-stack framework for MCP Apps — and the ChatGPT Apps SDK.

Build type-safe MCP servers whose tools render interactive React views inside Claude, ChatGPT, VS Code, Goose, and any other MCP-Apps-compatible host.

a fork of alpic-ai/skybridge · powered by

Account-free by design

Local dev, public tunneling, and deploy all work with no account, no token, and no vendor lock-in:

• Account-free tunneling via srv.us — open and SSH-based, no signup. enpilink dev --tunnel gives you a public /mcp URL in seconds and auto-generates an SSH key at ~/.enpilink/id_ed25519 the first time.
• No telemetry — zero analytics, no network calls, no embedded keys.
• Deploy anywhere — enpilink build produces a standard Node server (node dist/__entry.js); self-host on any platform or container.
• All five mcp-ui interaction types — tool, prompt, link, intent, and notify.

MCP Apps compliance

enpilink is a compliant MCP Apps framework, built on the official @modelcontextprotocol/ext-apps extension (stable spec 2026-01-26). It serves view resources for both runtimes so the same view runs in either host:

• ui://views/ext-apps/* — MCP Apps (Claude, Goose, VS Code, …)
• ui://views/apps-sdk/* — ChatGPT Apps SDK

The mcp-ui interaction types

An interaction type is one of the structured messages a view sends back to its host. The mcp-ui standard defines five, and enpilink supports all five (views send them through hooks, never raw postMessage):

| Type | Hook | Behavior | |---|---|---| | tool | useCallTool | real on both runtimes | | prompt | useSendFollowUpMessage | real on both runtimes | | link | useOpenExternal | real on both runtimes | | intent | useIntent | no spec equivalent on either runtime; best-effort extension, may no-op on hosts that don't route it | | notify | useNotify | real MCP notifications/message on MCP Apps; best-effort extension on the ChatGPT Apps SDK |

These five are the standard's view→host actions. They're a subset of the full hook API below (the rest of the hooks read host context or control your own view). New to all this? See PRESENTATION.md for a plain-language, diagram-led tour.

notify and intent are guarded and additive: they never throw and degrade to a no-op (or a log line) on hosts without support. See docs/guides/interaction-types.mdx for the full per-runtime matrix.

All view hooks

Everything a view can do from inside the iframe — import from enpilink/web. Hooks never touch raw postMessage; the bridge picks the right runtime call.

| Hook | What it does | Runtime | |---|---|---| | Interaction | | | | useCallTool | Call a server tool from the view; returns { callTool, callToolAsync, data, status, error } with pending/success/error state. | both | | useSendFollowUpMessage | Send a text message to the model as a user follow-up turn (prompt). | both | | useNotify | Surface a notification/status to the host: notify({ message, level?, title?, data? }). | both — real notifications/message on MCP Apps, best-effort on Apps SDK | | useIntent | Express a high-level intent for the host to route: sendIntent({ name, params? }). | both — best-effort extension, may no-op | | Navigation / links | | | | useOpenExternal | Open a URL outside the iframe via the host (use instead of window.open). | both | | useSetOpenInAppUrl | Override the URL the host's fullscreen "Open in app" affordance points to. | Apps SDK only (throws on MCP Apps) | | useRequestClose | Ask the host to dismiss/close the view. | both | | Layout / display | | | | useDisplayMode | Read and request the display mode — inline / pip / fullscreen. | both | | useRequestModal | Open the view in a host modal overlay; returns { isOpen, params, open }. | both | | useRequestSize | Ask the host to resize the iframe to fit your content. | both | | useLayout | Read the visual environment — max height, safe-area insets, theme. | both | | Context / data | | | | useToolInfo | Read the typed input / output / metadata of the tool call that rendered this view. | both | | useViewState | [state, setState] persisted on the host across remounts of the view. | both | | useUser | Session-stable user/environment info (device type, hover/touch capability). | both | | Files | | | | useFiles | Host file operations — upload, getDownloadUrl, selectFiles (native picker). | Apps SDK only (throws on MCP Apps) | | useDownload | Download an MCP EmbeddedResource / ResourceLink's contents via the host. | both | | Advanced | | | | useRegisterViewTool | Let the view expose its own tool to the host/model (app-provided tool). | MCP Apps only (no-op on Apps SDK) |

"both" = works on MCP Apps (Claude, Goose, VS Code…) and the ChatGPT Apps SDK. Apps-SDK-only hooks throw on MCP Apps; MCP-Apps-only hooks no-op on the Apps SDK.

Observability & Admin

enpilink ships an opt-in observability + admin layer — off by default, with zero overhead and zero network when disabled (still no telemetry to us).

• Observability — set ENPILINK_ANALYTICS=1 to record per-tool-call volume, latency (p50/p95/p99), and error rate, viewable in the Console Dashboard with a live log stream. Try it with demo data: enpilink dev --mock (deterministic, in-memory, no real traffic). See docs/guides/observability.mdx.
• Configuration — a typed config layer with env > file > DB precedence, a Configuration admin tab for runtime settings, env-only masked secrets, and a change audit log. See docs/guides/configuration.mdx.
• Admin (production) — expose the Dashboard + Configuration in prod with enpilink start --admin + ENPILINK_ADMIN_TOKEN (refuses to start without a token). Two-tier auth keeps /mcp and the SPA shell public while gating the data APIs behind a static bearer token; for SSO, front it with a reverse proxy (Cloudflare Access / oauth2-proxy / Tailscale) or self-hosted OIDC. See docs/guides/admin.mdx.
• Storage — pluggable adapters: memory (dev), sqlite (prod default, ENPILINK_DB_PATH), postgres (ENPILINK_DB_URL/DATABASE_URL/PG*), plus registerStorageAdapter for custom backends, and optional OpenTelemetry metrics export (ENPILINK_OTEL=1 + OTEL_EXPORTER_OTLP_ENDPOINT). See docs/guides/storage.mdx.

Documentation

New here? Read PRESENTATION.md first — a plain-language, diagram-led tour of the whole platform (what it solves, the standards, the technology, and how interaction types relate to hooks). No prior knowledge needed.

There's no hosted docs site yet — the full docs run locally with Mintlify:

pnpm install
pnpm docs:dev          # serves the docs at http://localhost:3000

What's inside docs/:

• API reference (docs/api-reference/) — a page per hook and core API (useCallTool, useNotify, useViewState, registerTool, …), each with the signature, a runnable example, and runtime support. This is the "what can I actually do with this hook" reference.
• Guides (docs/guides/) — task-oriented: communicating with the model, managing state, host-environment context, fetching data, the interaction types, and the observability / configuration / admin / storage layer.
• Concepts & fundamentals — MCP Apps vs the Apps SDK, write-once-run-everywhere, type safety, and data flow.
• Quickstart — create a new app, add to an existing server, deploy, migrate.

Tip: you can also read any page directly as Markdown in docs/ on GitHub — e.g. docs/api-reference/use-notify.mdx.

Quickstart

Prerequisites

• Node.js ≥ 22
• ssh (ships with macOS/Linux) — only needed for --tunnel

Run the built-in kitchen-sink demo

The fastest way to see everything is the bundled kitchen-sink showcase (a fictional store, Northwind): 9 tools, 9 views, all 4 interaction types, every host hook, deterministic mock data.

git clone https://github.com/enpitech/enpilink
cd enpilink && pnpm install && pnpm run build

cd examples/kitchen-sink
pnpm dev          # Console + HMR at http://localhost:3000/
pnpm dev:tunnel   # opens an account-free srv.us tunnel and prints a public /mcp URL

Then connect it to Claude:

1. Copy the printed https://<hash>.srv.us/mcp URL.
2. In Claude → Settings → Connectors → Add custom connector, paste that URL.
3. Paste the contents of examples/kitchen-sink/specs/SYSTEM_PROMPT.md into your Claude project instructions (MCP can't set a host system prompt, so this tells the assistant which tools to call).

Scaffold a new app

npm create enpilink@latest my-app

POC distribution caveat. enpilink and @enpilink/console are not yet published to npm, so a freshly scaffolded app's npm install will fail on the workspace:* ranges in the templates. For real distribution, publish both packages to npm and run node scripts/bump.js <version> to rewrite the templates' workspace:* ranges to ^<version>. Until then, scaffold inside this monorepo (the templates resolve via the workspace) or use local pnpm pack tarballs. See Status below.

The account-free tunnel under the hood is just one SSH command:

ssh srv.us -R 1:localhost:<port>

enpilink wraps this with auto key-gen (~/.enpilink/id_ed25519), URL parsing, and auto-reconnect.

CLI

enpilink dev [--tunnel] [-p <port>] [--open] [--mock]   # dev server + Console + HMR (alias: enpi)
enpilink build                                           # compile server + views → dist/
enpilink start [--admin]                                 # run the production build (node dist/__entry.js)
enpilink create [dir]                                    # scaffold a new app (passthrough to create-enpilink)

Production gotcha

The production entry reads the __PORT environment variable (NOT PORT), defaulting to 3000:

__PORT=8080 node dist/__entry.js

enpilink start sets __PORT for you. enpilink build also rewrites server @/… path aliases automatically, so you do not need tsc-alias in your own build scripts.

Repo layout

enpilink/
├── packages/
│   ├── core/             → npm "enpilink": server framework + React hooks + Vite plugin + CLI (oclif + Ink)
│   ├── console/          → "@enpilink/console": dashboard / config / playground / docs web UI
│   └── create-enpilink/  → "create-enpilink": scaffolder (templates: blank, demo)
├── examples/
│   ├── kitchen-sink/     → the all-features showcase ("Northwind"); basis of the demo template
│   └── manifest-ui/      → minimal single-view smoke-test example
├── docs/                 → Mintlify documentation
├── skills/               → agent skill for building enpilink apps
└── scripts/              → version bump / overrides helpers

Status

This is a POC fork. Today:

• ✅ Local dev, Console, HMR, build, and self-host all work account-free.
• ✅ The account-free srv.us tunnel is live-verified end-to-end (the printed /mcp URL round-trips over a real public tunnel and survives reconnects).
• ⏳ Real npm distribution requires publishing enpilink + @enpilink/console to npm, then running node scripts/bump.js <version>. Until then, npm create enpilink is workspace-linked (works inside this repo / via local tarballs, not from a bare npm install).

Attribution & license

enpilink is released under the MIT License. It is forked from alpic-ai/skybridge (MIT); the original copyright is retained in LICENSE, and the fork's changes are summarized in NOTICE.

Built and maintained by the Enpitech team.