About Web Viewer apps

An Agentic Development Toolkit (ADT) Web Viewer app is a modern web interface running inside a FileMaker Web Viewer. The web layer handles the UI. FileMaker still provides the data, security, scripts, file system access, printing, and deployment environment.

This section covers the hybrid app model in depth: why it works, how the pieces connect, how the dev-time bridge and runtime bridge behave, how FileMaker scripts act as your backend, and how a built app actually gets into FileMaker.

Note  New to ADT? Start with Install and Connect for the recommended setup path, or Build a Web Viewer App for the guided walkthrough. Use this section to go deeper on the hybrid app model itself.

• Why Web Viewer apps? — Learn why a Web Viewer app is a practical architecture, not just an escape hatch.

• How ADT connects to FileMaker — See how the coding agent, MCP server, Agent Access, ADT's components, FileMaker file, and Web Viewer connect.

• fmBridge() — Understand the dev-time bridge that lets your app run in a real browser while talking to a live FileMaker file.

• Call FileMaker scripts from an app — Treat FileMaker scripts as your API layer, running with the user's own permissions.

• How embedded deployment works — See what deploying a Web Viewer app actually means and where the built bundle lives.

• Runtime platforms and limitations — Read the platform-specific quirks and limits worth knowing before you build.

The short version

Think of the Web Viewer as the interface layer and FileMaker as the application platform underneath it.

• The user interacts with a React UI running in the Web Viewer.

• The web app calls FileMaker scripts when it needs data or business logic.

• Scripts read and write the database with the user's FileMaker permissions.

• Scripts can also call external APIs, access files, generate PDFs, and use plugins.

The bridge that makes this possible is not a separate npm package — it's the runtime layer built into @adt/fmdapi, the library adt app add vendors into the project at vendor/@adt/fmdapi (one shared copy per project) the first time you create a Web Viewer app. It handles both sides of the connection: a dev-time bridge so your app can run in a real browser against a live FileMaker file, and a runtime adapter that turns your app's data calls into requests a FileMaker script can execute. See Overview for the full reference.

Start with Why Web Viewer Apps? for the concept, then read How ADT Connects to FileMaker to see how the pieces fit together.