Blog
Notes on B4.run
Writing on the agent stack, type-safety, and the tools we're building.
Essay · 12 min read
What is a software factory?
Software factory is a buzzword again. Here is what the term meant in 1968, what it means in 2026, and what we learned building one with B4.run.
B4.run 0.13: A sandbox per thread
Learn what 0.13 adds for threads that need their own environment: per-thread images and permissions, staged workspaces and HTTP reads.
B4.run 0.9 to 0.12: The answer the user sees
Learn what 0.9 through 0.12 changed about the final answer: response schemas, an after hook, returnDirect tools and streamed tool arguments.
Essay · 23 min
Build a code-fixing agent you can read
Follow a B4.run agent from a failing CLI test through a Docker workspace, independent checks, and approval of the exact change.
B4.run 0.8: The framework around the agent
Learn what 0.5 through 0.8 added around the agent: evals, tool permissions, sandboxes, delegation, typed memory, AG-UI clients and production builds.
Essay · 9 min
B4.run at the edge: The Hono target
B4.run's opt-in Hono target emits a Node-free Cloudflare Workers entry with request-scoped Postgres stores and a tested workerd subset.
Essay · 6 min
Eve and B4.run: Choosing an agent framework
Eve and B4.run both organize agents as files. Here is what that structure gives us, and how to compare the client, runtime and deployment choices.
B4.run 0.4: Start with an agent test
Learn how the offline agent test added to the starter in 0.4 works, and what a scripted model response can verify.
Essay · 7 min
The App Router for AI Agents
Learn how B4.run uses file-system routes, typed tools, planning, skills and subagents to organize a LangGraph.js agent application.
Essay · 7 min
Why we built B4.run
B4.run is a TypeScript framework for LangGraph.js agents. Here is the problem it solves and its conventions: file-system routes, local tools and typegen.
Build your own agent.
Scaffold a project and walk through every file it gives you.