MCP app builder: a Claude connector that builds apps
Exotool is an app builder you use from Claude. It connects to Claude through MCP, the open standard for giving an AI assistant tools, and the tools it gives Claude create, read, change and build Exotool apps. Claude edits the app's diagram; Exotool's patented engine generates the app from it. You get a working progressive web app, server side included, and the generated source to run where you choose.
What MCP is
The Model Context Protocol (MCP) is an open standard, started by Anthropic, through which an assistant such as Claude is given tools by an outside service: the service describes its tools, Claude calls them during a conversation, and the results come back into the chat. In Claude these services appear as connectors, listed in the Claude directory or added by their address. An MCP app builder is such a service whose tools build apps.
How Exotool's connector works
Connected and signed in, Claude holds a set of tools for your Exotool account: list your projects, create a project or copy a sample, load a project's diagram, patch it or save it back (which compiles the app), check it for build errors, upload an icon, an image or a file, read the Exotool references, and give you the preview and editor addresses. Claude reads the references first, plans the change, and makes it as a change to the diagram. Every save is backed up before it happens, so a change can be undone; a stale change (you edited the diagram meanwhile) is refused rather than overwriting yours; server-side code Claude authors is shown to you before it is saved. The full list is in the tool reference.
What makes it different from a code-writing AI builder
| A code-writing AI builder | Exotool through MCP | |
|---|---|---|
| What the model produces | Source code, different each time. | A change to a diagram. |
| What builds the app | The model. | A patented engine, from the diagram, the same way every time. |
| What you review | Thousands of generated lines, or the running app. | One diagram, in the editor, with the changed elements shown. |
| Where the AI runs | Inside the builder, metered in credits or tokens. | In your own Claude account; Exotool meters nothing. |
| Where the app runs | On the builder's platform, usually. | In Exotool's sandbox while you build; then on a host of your choice. |
| What you keep | Often the code; sometimes nothing. | The code, the diagram and your database. |
| The database | Often reached from the browser with a client key; per-row rules are the guard. | Reached only from the server side the engine generated; the browser is never given a database key. |
| Debugging | Browser tools for the client; the backend service's logs for the rest. | One debugger over both ends: a step is followed from the device to the server and back. |
Who it is for
- People who have never built an app. Describe it; open the result on your phone; read the diagram when you are curious. The free plan is enough to start.
- Builders who use the Exotool editor. Ask Claude for the tedious parts and keep the design in your hands; Claude sees your changes the next time it loads the diagram.
- Teams that must know what was built. The diagram is the audit trail: no generated code to read to find out what the app does.
- Experienced developers. The activity language takes explicit JavaScript and PHP wherever you
want it (a
JS< >JSorPHP< >PHPblock, as an expression or a statement), so you write the parts that need your hand and let Exotool generate and knit together the rest of the stack: a front end in minutes, with the server side and the APIs made for it. And you debug both ends at once: the visual debugger follows a step from the device to the server and back in one session, breakpoints and variables on either side, which is extraordinarily hard to do by hand in a client/server app.
The split that keeps data safe
Exotool's patented engine decides what runs on the device and what runs on the server, and generates the APIs between them. The database is addressed only from the generated server side; the browser never holds a database key, and the device side gets only what the server side sends. In many AI builders the app talks to its database from the browser, a client key in hand, with per-row rules as the only guard: one missing rule and a table is public. A 2025 scan of 1,645 apps built with one such builder found 170 with exposed tables (CVE-2025-48757), and Bubble's own documentation warns that a data type with no privacy rule is readable by everyone. With Exotool there is no such rule to forget. If a value must never reach the device at all, you say so, and the engine keeps it on the server.
Connect it
- Open Exotool in the Claude directory and choose
Connect, or add a custom connector in Claude's settings with the address
https://mcp.ops.exotool.com/mcp. - Sign in with your Exotool account; the sign-in page can create one.
- In a new chat:
Build me a simple picture database app.
The step-by-step page: build an app with Claude. The connector's documentation: the Exotool MCP server for Claude.