Vessel — send a tool like you'd send a spreadsheet
Open-source runtime · Chromium-first
Send a tool like you'd<br>send a spreadsheet.
The artifact format for AI-generated software : describe a tool, and the model hands you one<br>self-contained .vessel — UI, logic, and data inside — that runs the instant you open it, with<br>nothing to deploy or operate. Install the host once; any .vessel then opens by double-click,<br>runs, and saves back into the same file.
Get the host →<br>Run it yourself
Installs as a PWA — runs locally, works offline after the first load (no server). Promptless save on<br>Chromium; Firefox & Safari run degraded (open + download-to-save). ·<br>Docs →
model.vessel
ui React interface
app FastAPI · Python
data SQLite database
everything inside one passable file
The spreadsheet model, for web tech
01<br>Install the engine once
The host is a small installable PWA. You set it up a single time — like installing a spreadsheet app.
02<br>The file carries everything
A .vessel is an OPC-style ZIP (think .xlsx). UI, backend, and data travel together.
03<br>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
ui<br>React, sandboxed
The bundle's interface renders in a sandboxed, opaque-origin iframe — isolated from the host and from your machine.
app<br>Python in WASM
An ordinary FastAPI backend runs in Pyodide (CPython compiled to WebAssembly). fetch is bridged straight to ASGI.
data<br>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<br>the host's light/dark and chosen theme automatically. Switch them here and watch it re-theme live:
budget.vessel
Theme
Default<br>Slate<br>Warm
☾ Dark
The same tokens a bundle reads — see<br>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<br>UI, declared packages. Hand your AI agent the Vessel authoring skill and it produces valid bundles, correct<br>manifest and all.
Copy<br>Follow the Vessel authoring skill, then build me a .vessel tool:<br>https://getvessel.dev/skills/vessel-author/SKILL.md
Paste that into Claude or your agent, or<br>read the skill.<br>Prefer a CLI? npm i -g vessel-cli, then vessel new /<br>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<br>yourself and it runs identically (and offline). Same code, your origin.
Copy<br>git clone https://github.com/apollo-orbit-dev/vessel.git<br>cd vessel<br>npm install<br>npm run build -w @vessel/host<br>npm run preview -w @vessel/host
Then open the printed http://localhost:4173/app/ in Chromium and install the PWA —<br>localhost is a secure context, so file handling + install work. Full guide in the<br>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<br>default-deny network egress and a manifest allowlist. The host never hands its writable file handle to bundle<br>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<br>create / edit / delete. Download one and open it in the host. The last five are aimed at developers.
Budget<br>unsigned
Local-first money — transactions, categories, a trend + forecast chart.
Download .vessel ↓
Flashcards<br>unsigned
SM-2 spaced repetition — edit the deck, study, and rate.
Download .vessel ↓
CSV Explorer<br>signed · Tabula Labs
Real SQL filter/sort over thousands of rows; import your own CSV.
Download .vessel ↓
Invoice<br>signed · Ledgerleaf
A fully editable invoice template with live totals and print-to-PDF.
Download .vessel ↓
Recipe Planner<br>unsigned
Recipes plus a weekly plan; a shopping list built from the plan.
Download .vessel ↓
Habits<br>unsigned
A 21-day habit grid with streaks you tick off day by day.
Download .vessel ↓
Personal CRM<br>unsigned
Contacts with a genuine “haven’t talked in 90 days” SQL query.
Download .vessel ↓
Job Tracker<br>unsigned
A pipeline board: Applied → Screen → Onsite → Offer.
Download .vessel ↓
Workout Log<br>unsigned
Sets, PRs, reusable routines, and a training-volume chart.
Download .vessel ↓
Journal<br>unsigned
A dated journal with SQLite full-text search and match highlighting.
Download .vessel ↓
SQLite Playground<br>unsigned
Open any .sqlite file — browse tables, run SQL, see an auto-generated ER diagram.
Download .vessel ↓
Regex Tester<br>unsigned
Test patterns with the real Python re engine; save a pattern library that travels in the file.
Download .vessel ↓
JWT Inspector<br>unsigned
Decode and verify JWTs (HMAC + RSA/ECDSA) locally — the token never leaves the...