# Show HN: Vessel – Portable app files (UI, FastAPI, SQLite) like .xlsx for tools > Source: > Published: 2026-06-18 12:35:19+00:00 ### React, sandboxed The bundle's interface renders in a sandboxed, opaque-origin iframe — isolated from the host and from your machine. Open-source runtime · Chromium-first 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. 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 →](https://github.com/apollo-orbit-dev/vessel) The spreadsheet model, for web tech The host is a small installable PWA. You set it up a single time — like installing a spreadsheet app. A `.vessel` is an OPC-style ZIP (think `.xlsx` ). UI, backend, and data travel together. Double-click to run. Changes write straight back into the file — no export step, no server, no account. What's inside the box The bundle's interface renders in a sandboxed, opaque-origin iframe — isolated from the host and from your machine. An ordinary FastAPI backend runs in Pyodide (CPython compiled to WebAssembly). `fetch` is bridged straight to ASGI. 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: The same tokens a bundle reads — see [the authoring skill](https://github.com/apollo-orbit-dev/vessel/blob/main/skills/vessel-author/SKILL.md). 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](https://github.com/apollo-orbit-dev/vessel/blob/main/skills/vessel-author/SKILL.md). 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](https://github.com/apollo-orbit-dev/vessel). 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. Local-first money — transactions, categories, a trend + forecast chart. Download .vessel ↓SM-2 spaced repetition — edit the deck, study, and rate. Download .vessel ↓Real SQL filter/sort over thousands of rows; import your own CSV. Download .vessel ↓A fully editable invoice template with live totals and print-to-PDF. Download .vessel ↓Recipes plus a weekly plan; a shopping list built from the plan. Download .vessel ↓A 21-day habit grid with streaks you tick off day by day. Download .vessel ↓Contacts with a genuine “haven’t talked in 90 days” SQL query. Download .vessel ↓A pipeline board: Applied → Screen → Onsite → Offer. Download .vessel ↓Sets, PRs, reusable routines, and a training-volume chart. Download .vessel ↓A dated journal with SQLite full-text search and match highlighting. Download .vessel ↓Open any `.sqlite` file — browse tables, run SQL, see an auto-generated ER diagram. Test patterns with the real Python `re` engine; save a pattern library that travels in the file. Decode and verify JWTs (HMAC + RSA/ECDSA) locally — the token never leaves the file. Download .vessel ↓Convert & validate JSON / YAML / TOML, with a path query — all on your machine. Download .vessel ↓A mini-Postman whose Python backend makes the real calls (no CORS wall); collections live in the file. Download .vessel ↓ Need the host first? [Get it →](/app/) · or [read the source](https://github.com/apollo-orbit-dev/vessel/tree/main/examples). See it running Real `.vessel` tools open in the host — same chrome, your data inside the file.