TypeScript meta-framework for LangGraph.js

Build LangGraph agents like Next.js apps.

B4.run adds file-system routes, shared and route-local tools, generated types, deterministic tests, durable threads, and build targets around LangGraph.js. Keep the runtime. Drop the boilerplate.

Get started · Migrate from LangGraph.js · Documentation · Discussions

npm create b4-app@latest my-agent

Read the product-loop transcript.

Quickstart

The first activation is the no-key path:

Requires Node.js 24 or later.

npm create b4-app@latest my-agent
cd my-agent
npm install
npm test

In a credential-sanitized clean-room run on August 31, 2026, npm resolved create-b4-app 0.8.21; the generated starter installed and its default fixture suite passed, with one opt-in test file skipped. The observation is version- and date-specific; @latest can move. See the activation receipt.

Why B4.run

• Author the application shape, not route wiring. Put one supported entry in a route's src/app/**/index.ts; B4.run discovers the route. Shared tools live in src/tools/, while route-local tools can live beside the route and remain subject to its runtime policy.
• Let generated types follow the route. B4.run generates TypeScript route, parameter, state, and tool declarations during typegen and build. State types are emitted when the discovered state schema supplies valid defaults.
• Make the normal test loop deterministic. Fixture-backed tests replay committed responses and fail on an unmatched interaction instead of silently calling a provider. Live and recording modes remain explicit opt-ins.
• Carry one project from local state to build artifacts. Default SQLite-backed state can survive a b4 dev restart when the app root and its SQLite files persist. The default build emits a runnable Node server, Dockerfile, and LangSmith graph artifacts; validate the runtime, storage, auth, and provider boundary for the deployment target you choose.

How B4.run fits

What B4.run writes for you

Already have a graph? Keep its nodes, edges, and imports, expose it as a raw graph route, and validate invocation and checkpointer behavior for each target. The full migration guide covers that incremental path.

What are you building?

• Research assistant
• Chat and workspace assistant
• Memory-backed agent
• Routes and workflows guide

When B4.run fits

• A good fit: a TypeScript team wants LangGraph.js with file-system routes, generated types, a local test and development loop, persistence primitives, and build targets. Capability support varies by target, so validate the subset your application uses.
• Stay with raw LangGraph.js: if you do not want B4.run's application conventions, or if your project requires Python. B4.run requires LangGraph.js and targets TypeScript and Node.js.
• Bring the ecosystem with you: existing raw LangGraph.js graphs can migrate incrementally as graph routes. LangChain remains usable, and CopilotKit composes with B4.run through the tested AG-UI boundary; validate versions and target-specific invocation, provider, and checkpointer behavior in your app.

B4.run is not a hosted AI platform or an infrastructure provisioner. You operate the emitted application or deploy it through a separate platform.

Build with a coding agent

Give your coding agent the framework sources before it writes a route.

Scaffold a new B4.run app and help me build an agent. B4.run is the TypeScript meta-framework for LangGraph — agents and workflows are file-system routes with route-local tools, generated types, and durable threads. Run `npm create b4-app@latest my-agent` to scaffold, then read https://b4.run/AGENTS.md and https://b4.run/llms-full.txt for the full framework reference before writing any routes.

Run it live

Credentials are provider-specific: the published research starter's OpenAI live path requires OPENAI_API_KEY, while a local Ollama route requires no provider key.

Published @latest (0.8.21)

The clean-room activation recorded above resolved npm @latest to 0.8.21. That published scaffold is a single package. Set its OpenAI key and start its B4.run server on port 3000:

export OPENAI_API_KEY=sk-...
npm run dev

Drive the backend through the Agent Protocol, or follow the Workbench guide to add a browser client; the 0.8.21 scaffold does not include the Workbench package.

In a clean 0.8.21 scaffold inspected on September 1, 2026, npm run build compiles the TypeScript project. That scaffold does not define npm start; use npm run dev for its working server path.

Current source (unreleased 0.8.22)

The current checked-in research template is a two-package workspace with a server and the B4.run Workbench. These commands apply to a scaffold generated from current repository source, not the published @latest package:

npm install
export OPENAI_API_KEY=sk-...
npm run dev:server

In a second terminal:

npm run dev:web

That source template serves the B4.run server on port 3002 and the Workbench on port 3010. Its root workspace defines the production build and start scripts:

npm run build
npm start

Choose and validate the deployment boundary that matches your application: Node, LangSmith, edge targets, or Kubernetes. B4.run emits the artifacts; it does not provision infrastructure, host the application, or manage its secrets.

Maturity and support

B4.run is pre-1.0 and its API surface is moving. Pin versions and read the release notes and upgrade guide. Supported means documented public surfaces on the current release line, not a 1.0 stability or long-term support guarantee.

• Follow SUPPORT.md for support routes, and ask usage questions in GitHub Discussions.
• Report security issues through the process in SECURITY.md.
• See CONTRIBUTING.md and CONTRIBUTORS.md before contributing.
• Follow the Code of Conduct.

Ready to start?

npm create b4-app@latest my-agent

License

MIT. See LICENSE.