# B4.run

An agent framework built on LangGraph.js that adds file-system based routes, generated TypeScript types, workspaces, sandboxed execution and approval flows, for building agents in TypeScript.

B4.run is a TypeScript framework for building AI agents on top of LangGraph.js. Agent routes are authored as files under an app directory and discovered automatically, with shared tools kept separate from route-local tools that stay under a route's own runtime policy.

It generates TypeScript declarations for routes, parameters, state and tools during typegen and build. Fixture-backed tests replay committed responses and fail on an unmatched interaction instead of silently calling a live provider, with live and recording modes as explicit opt-ins. Local state is SQLite-backed by default and can survive a restart of the development server.

The default build produces a runnable Node server, a Dockerfile and LangSmith graph artifacts. LangGraph.js remains the underlying graph runtime, and LangChain integrations remain available through the framework's built-in agent path.

Website: https://b4.run