Open-source runtime · Chromium-first

Send a tool like you'd
send a spreadsheet.

The artifact format for AI-generated software: describe a tool, and the model hands you one self-contained .vessel — UI, logic, and data inside — that runs the instant you open it, with nothing to deploy or operate. Install the host once; any .vessel then opens by double-click, runs, and saves back into the same file.

Get the host → Run it yourself

Installs as a PWA — runs locally, works offline after the first load (no server). Promptless save on Chromium; Firefox & Safari run degraded (open + download-to-save). · Docs →

The spreadsheet model, for web tech

Install the engine once

The host is a small installable PWA. You set it up a single time — like installing a spreadsheet app.

The file carries everything

A .vessel is an OPC-style ZIP (think .xlsx). UI, backend, and data travel together.

Open, edit, save in place

Double-click to run. Changes write straight back into the file — no export step, no server, no account.

What's inside the box

React, sandboxed

The bundle's interface renders in a sandboxed, opaque-origin iframe — isolated from the host and from your machine.

app

Python in WASM

An ordinary FastAPI backend runs in Pyodide (CPython compiled to WebAssembly). fetch is bridged straight to ASGI.

data

SQLite in the file

State lives in a real SQLite database — and that database travels inside the .vessel. The file is the document.

One theme system, every tool

Tools don't hardcode colors — they style with the host's --vessel-* tokens, so every tool follows the host's light/dark and chosen theme automatically. Switch them here and watch it re-theme live:

budget.vessel Theme

The same tokens a bundle reads — see the authoring skill.

Build one with your AI

Authoring a .vessel has a few non-obvious rules — an async-only Python backend, a single-file UI, declared packages. Hand your AI agent the Vessel authoring skill and it produces valid bundles, correct manifest and all.

Follow the Vessel authoring skill, then build me a .vessel tool:
https://getvessel.dev/skills/vessel-author/SKILL.md

Paste that into Claude or your agent, or read the skill. Prefer a CLI? npm i -g vessel-cli, then vessel new / dev / build.

Run it yourself

Prefer not to depend on getvessel.dev? The host is a static app with no backend — build and serve it yourself and it runs identically (and offline). Same code, your origin.

git clone https://github.com/apollo-orbit-dev/vessel.git
cd vessel
npm install
npm run build -w @vessel/host
npm run preview -w @vessel/host

Then open the printed http://localhost:4173/app/ in Chromium and install the PWA — localhost is a secure context, so file handling + install work. Full guide in the docs.

The safety claim

Opening a .vessel is no more dangerous than opening a web page.

Bundle code is boxed twice — a sandboxed iframe around the UI, a WASM sandbox around the Python — with default-deny network egress and a manifest allowlist. The host never hands its writable file handle to bundle code. Bundles can be Ed25519-signed so you can see who published them.

Fifteen example tools

Real .vessel files — each a FastAPI + SQLite backend and a self-contained UI, with full create / edit / delete. Download one and open it in the host. The last five are aimed at developers.

Budget

unsigned

Local-first money — transactions, categories, a trend + forecast chart.

Send a tool like you'dsend a spreadsheet.

Install the engine once

The file carries everything

Open, edit, save in place

React, sandboxed

Python in WASM

SQLite in the file

Budget

Flashcards

CSV Explorer

Invoice

Recipe Planner

Habits

Personal CRM

Job Tracker

Workout Log

Journal

SQLite Playground

Regex Tester

JWT Inspector

Data Converter

API Workbench

Send a tool like you'd
send a spreadsheet.