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- Sandcastle is Matt’s open-source TypeScript framework for orchestrating parallel sandboxed coding agents: each agent runs in Docker (or Podman/Vercel), receives a worktree, executes, and patches commits back to the host when done. The
sandcastle.run() function is the single entry point — low-ceremony by design. - Key workflow: Sandcastle reads a backlog of issues, spawns N Claude agents in isolated Docker containers on separate git worktrees, each tackling one issue, then merges all successful worktrees back to a target branch. Entirely AFK; the developer reviews the merge, not the execution.
- The meta-demonstration: Sandcastle itself was built with 889 commits, none hand-coded. Matt used his own skills system to generate the specs; Sandcastle executed them. Self-dogfooding as validation.
- Practical takeaway: if you want parallel AFK agent execution with complete data isolation (everything stays local, no cloud inference) and TypeScript-native orchestration, Sandcastle is the current reference implementation for that pattern.