Try it
Run the Playground in a browser tab, or download the desktop app for the fully private experience. Start with the five-minute quickstart.
Snug Protocol documentation
MCP connects agents to tools. Snug connects agents to apps.
Snug is an open protocol for tiny, user-built apps that think through their host’s AI agent
at runtime. A Snug app is a small sandboxed app — usually one HTML file — created through
conversation. At runtime it exchanges versioned JSON envelopes with the host agent: the
agent is the app’s mind, the app is a body. Users own everything as one portable .snug file.
Build an app
You mostly talk — the agent writes the app. Understand what it produces in Build your first app.
Implement the protocol
Host Snug apps in your own product or build a hub client from scratch: Implementor quickstart.
Read the spec
The complete 1.0 specification — wire protocol, portable user database, connected apps, runtime contracts — plus JSON Schemas for every frame.
The shape of the system
Section titled “The shape of the system”Three actors, deliberately separated:
- The user owns ONE portable SQLite file (
.snug) holding every app, its data, its chats, and its settings. It runs from a browser (OPFS) or a desktop disk, syncs where the user chooses, and exports whole. - The hub client (a web app, a desktop shell, your product) renders apps in a hard sandbox and brokers every capability: agent turns, storage, network, navigation.
- The LLM provider is whatever the user or host picks — the protocol is provider-neutral, and a well-built app runs on a frontier model or a small local one.
Security is architectural, not policy: app iframes get no network of their own, and credentials never enter the app, never reach the LLM, and never reach a publisher. The whitepaper argues the design; the spec makes it normative.
What is Snug?The ten-minute mental model — bodies and minds, envelopes, the user file.