open-mcp-apps

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Give your AI a persistent, reusable UI. It builds the app once — you keep it forever.

open-mcp-apps is an open engine built on MCP Apps (ui://, SEP-1865) — one of the two official extensions to the Model Context Protocol, adopted into the protocol’s new Extensions Track. It gives any MCP-Apps-capable host (Claude Desktop, claude.ai, Codex, ChatGPT, …) three things the extension itself doesn’t provide:

1. An app registry the AI can write to. Ask for a UI that doesn’t exist — the AI reads the authoring guide, writes a single-file HTML app against a tiny window.oma API, and saves it. From that moment open_ is a tool, in this chat and every future one.
2. Persistent, versioned data — separate from the UI. Apps bind to generic collections of items backed by SQLite plus an append-only change_event ledger. Every mutation is an idempotent domain command (command_id) with optimistic concurrency (expected_version). The AI and the human edit the same store — the widget is just a view.
3. A shell runtime so AI-written apps actually work. Serving ui://, the engine wraps the app with the official MCP App bridge, host theming (Claude’s design tokens, light/dark), and the window.oma data API. What you write is a view; the protocol, persistence, idempotency and theming are the engine’s problem.

The loop

"make me a kanban"
      │
      ▼
list_apps ── exists? ──► open_kanban          (reuse, instant)
      │ no
      ▼
get_app_guide ──► AI writes HTML ──► save_app
      │
      ▼
open_kanban  →  rendered inline, themed, persistent — reusable in every future chat

Apps accumulate. Each one is single-purpose and independent — a board, a tracker, a splitter — minted for the task in front of you and kept for the next time you need it.

What it looks like

Apps render inline, in the chat you were already having. Ask for one and the AI writes it:

Come back in another chat — or another host — and it’s still there, with your data in it:

The built-in library ships 17 ready-made apps — real, working previews, installed in a click:

Every app above is a single HTML file bound to plain data collections — written with the same window.oma API and authoring guide your AI will use for the apps it builds you.

Install

open-mcp-apps runs as a local MCP server. First get it connected to your host (below); then onboarding happens inside the host, separately — that’s where the AI builds your first app. Installing needs a shell, so the chat apps (Claude Desktop, Codex) can’t install themselves — use one of these:

As a user — one command:

curl -fsSL https://raw.githubusercontent.com/2nd1st/open-mcp-apps/main/install.sh | sh

It opens a short picker to choose which hosts to register into — Claude Desktop, Claude Code, Codex — plus your permission preference. Skip it with -s -- --yes, or target one host with -s -- --host codex. (Or clone and run it yourself: git clone https://github.com/2nd1st/open-mcp-apps && cd open-mcp-apps && node install.mjs.)

A note on npm: the open-mcp-apps package on the npm registry is not this project — that name is held by an unrelated package. Install from this repository, using the command above.

With a coding agent (Claude Code, Codex CLI — they have a shell), paste:

Read https://raw.githubusercontent.com/2nd1st/open-mcp-apps/main/install.md and follow it.

Either way, install.mjs registers the server into each host you pick (Claude Desktop, Claude Code, Codex), idempotently — it never clobbers your other servers, pins a stable node launcher (native SQLite ABI), reports what changed, and cleans up a pre-rename entry if one lingers. Your data lives in a fixed per-user store (not inside the clone), so every host shares the same apps and data. After installing or updating, fully quit and reopen the host (Cmd-Q, not just close the window) — it keeps its old server process on the old data until fully quit. Remote / one-click install (no shell) is coming later.

Uninstall: node uninstall.mjs unregisters the server from every host it finds — but keeps your data: the shared store stays put, so re-installing later restores every app and all data. Add --purge to also delete the shared store (irreversible), or --check to preview what would happen without changing anything:

node uninstall.mjs           # unregister from all detected hosts — keeps your data
node uninstall.mjs --purge   # also delete the shared store (apps + data), irreversible
node uninstall.mjs --check   # read-only: show what's registered and what would change

Reset escape hatch: the whole store is one SQLite file, open-mcp-apps.db, in ~/Library/Application Support/open-mcp-apps/ (macOS), %APPDATA%\open-mcp-apps\ (Windows), or $XDG_DATA_HOME else ~/.local/share/open-mcp-apps/ (Linux). Fully quit your host(s), delete that file (plus its -wal/-shm siblings), and you start clean — all apps and data gone, irreversibly, while staying installed.

Then get started — in your host. Restart it. New here? Tell the AI something like “I just installed open-mcp-apps — show me how to use it with a couple of examples, and suggest a few apps that fit how I work.” It reads what it can build, draws on what it knows about you (your memory and past chats — or it asks a couple of questions), and sets up a first app or two tailored to you. This step is separate from install and lives in the host. Or just ask directly:

• “make me a board for what I’m juggling right now” → the AI writes it, seeds it, and opens it (persistent)
• “make me a habit tracker” → watch it read the guide, write the app, save it, open it
• close the app, reopen, ask again → everything is still there

First-run permissions: the first few tool calls each show an approval dialog — pick “Always allow”. The tool set is small and stable on purpose: read-only tools generally skip approval, and the single open_app tool covers opening every app (including ones the AI creates later), so after those first clicks it’s zero-prompt forever. You can also batch it in Settings → Connectors → open-mcp-apps → Tool permissions. Note: a Desktop auto-update occasionally resets these decisions (upstream #56954) — just re-allow. Multiple widgets in one conversation work fine (habit-streaks + meal-planner side by side).

The browser viewer, and the port it binds

Every install runs a small local web server on ****. It is how you see your apps outside a chat window — one page per app, the same data your AI is reading — and in a terminal host it is the only way to see them at all, so the AI hands you the link when it builds or opens something.

It starts on its own. Two ways to change that:

OMA_VIEWER=0   # don't start it at all
PORT=9000      # start it somewhere else

Set either in the env block of your host’s MCP server entry. If the port is already taken by another open-mcp-apps process, that one is already serving the same data and this one just shares its address; if it is taken by something else, you get no viewer and no links rather than a link into a stranger’s server.

There is no password on it, and that is deliberate. The listener is hard-wired to 127.0.0.1, so there is no setting that makes it answer from another machine. Any program on your computer that could reach the port can already open the SQLite file directly — a password would be a lock beside an open wall. The one way this reaches the internet is a tunnel you start yourself, which is its own deliberate decision; while a tunnel is up, treat its URL as a secret, because it is currently the only thing standing between the internet and your data.

What’s in the box

npm test                     # every suite below, plus the static invariants and budget checks
node test/server-smoke.mjs   # 419 assertions over real stdio — incl. runtime app creation
node test/http-smoke.mjs     #  53 assertions over the HTTP transport (incl. SSE /events, viewer)
node test/provenance.mjs     #  39 assertions that an app's author — its trust tier — is not overwritable
node test/seed-smoke.mjs     #  14 assertions on the seed / design-kit pipeline
node test/files-smoke.mjs    #  45 assertions on the per-app file store (chunked uploads, GC races)

Writing an app yourself

The AI is the usual author, but it isn’t the only one — its context window shouldn’t be the ceiling on what an app can be. Build one in your own editor, with your own bundler, and install it:

node install-app.mjs ./my-app.html              # yours, full trust — same as an AI-authored app
node install-app.mjs ./my-app.html --sandboxed  # untrusted: runs behind the runner, no capabilities
node install-app.mjs --list                     # what's installed, and under whose provenance

One self-contained HTML document, ≤200 KB, no network requests — the engine injects the kit CSS, the host’s design tokens and window.oma. The trade: the AI can no longer iterate on it (your file is the source of truth, you rebuild and re-install), though it can still read the source, and the app shares your data like any other. Provenance is not overwritable in either direction, so an app installed --sandboxed stays sandboxed until you delete it.

RUNTIME.md is the contract — the window.oma API in both modes, what a sandboxed app can still do, and the traps that only bite authors who aren’t the AI. It carries a version (oma.contract) and test/runtime-contract.mjs pins it to the two runtimes’ real surfaces, so it can’t drift from them silently.

Design positions (why it’s built this way)

• UI and data persist separately, both versioned. Apps are views; collections are truth; the ledger is history. Swap either without losing the other.
• The AI talks domain commands, never SQL, never raw state. That’s what makes human+AI concurrent editing safe (idempotency + optimistic concurrency at the command layer).
• Extension-first. Everything rides the MCP Apps bridge — no host-private APIs. One codebase should serve every host that renders ui://.
• Single-purpose, not composite. Each app owns one scenario and its own collection; the engine mints a new one rather than cramming features into an old one. System apps (settings, dashboard) are the deliberate exception — engine-owned, privileged, allowed to see across collections.

Security model

Trust is tiered by where an app came from. Locally-authored and system apps run in direct mode. The engine also ships a runner — a sandboxed srcdoc iframe with a CSP-first document and a minimal read-scoped bridge — as the mandatory execution mode for any app that isn’t locally trusted, plus reserved security:* / policy:* config keys that generic data writes can’t touch and an out-of-band privileged writer.

Honest status: everything in the OSS version — your apps, AI-built apps, and the built-in library apps (all first-party) — runs locally in direct mode with full trust; there is nothing third-party to sandbox yet. The runner is built and tested but dormant: it is the ready seam for shared/published apps later, where review + sandboxing arrive together. See SECURITY.md for the full threat model and trust tiers.

Host support (live-tested 2026-07-22; ChatGPT web row updated 2026-07-28)

Everything rides the MCP Apps bridge, so host fixes upstream (e.g. #28912) benefit this project with zero changes.

On Codex specifically: plugins are registered on the web side, so a locally-installed engine is reached as an MCP server, not as a plugin — which is the right path for a self-hosted install anyway. Widget rendering in the ChatGPT desktop app also appears to depend on how you are signed in (we have seen it work under an account sign-in; not yet established under an API key).

Status / roadmap

Early v0 — proven end-to-end on Claude Desktop; cross-vendor render + shared store proven on Codex desktop and the browser viewer.

• [x] engine: registry + shell + generic data commands + ledger
• [x] system apps installed (settings, dashboard, library); 17 library apps with live previews, one-click install
• [x] AI app creation loop (guide → save → dynamic tool)
• [x] in-context onboarding (ask how to use it → the AI reads your history/memory and builds a tailored starter set)
• [x] security foundation: trust tiers + sandboxed runner + reserved config keys
• [x] multi-host discovery installer (Claude Desktop · Claude Code · Codex) + shared per-user store
• [ ] npx one-command install
• [ ] remote (Streamable HTTP) mode → claude.ai / ChatGPT / mobile
• [ ] app export/import → sharing → community library (review + runner sandbox activate here)

License

Two licenses, split by directory (LICENSING.md has the full map):

• The engine — everything outside components/ — is AGPL-3.0-only (LICENSE). Run a modified version as a network service and you must offer its source to your users (AGPL §13). Improvements to the engine stay open.
• The official apps in components/ — the apps you run and edit — are MIT (components/LICENSE). Open, copy, fork, and redistribute any app freely; changing your own dashboard is never a legal question.

The names open-mcp-apps, openmcp.app, SecondFirst, and 2nd1st, and their logos, are not granted by either license — see TRADEMARKS.md. Fork the code freely; give your fork its own name.

Copyright © 2026 2nd1st.

App contributions need nothing signed — MIT in, MIT out. For engine contributions, open an issue first: a CLA is intended but is still a draft (CONTRIBUTING.md · CLA.md).

© 2026 2nd1st