Show HN: Vessel – Portable app files (UI, FastAPI, SQLite) like .xlsx for tools

Vessel is a new portable app file format that bundles UI, FastAPI backend, and SQLite data into a single .vessel file, enabling AI-generated tools to run locally with no deployment. The open-source runtime installs as a PWA and sandboxes code in an iframe and WebAssembly for security.

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.