Sandcastle

Sandcastle is a TypeScript library for developers building automated coding workflows in scripts, CI pipelines, or custom tools. It coordinates sandboxed AI coding agents and manages where their Git changes land.

• Git branch management: Agents can edit the current working directory, use a temporary branch that merges back when finished, or commit to a named branch for further work.
• Parallel agents and reviews: You can coordinate unattended agents and build workflows that pass implementation work to a review agent.
• Reusable sandboxes: Multiple agent runs can share one environment and branch, retaining installed dependencies and build artifacts between runs.
• Verification and interactive sessions: Your workflow can run shell commands in the agent's sandbox to check its work before review, and you can also use interactive agent sessions.

Docker and Podman run the agent's tools in local containers. Their default branch behavior lets agents write directly to the host working directory, so container isolation doesn't imply a separate copy of your code. Vercel execution runs in cloud Firecracker microVMs. These sandbox choices determine where tools execute; they don't establish where a chosen agent runs model inference.

Sandcastle is open source under the MIT license and requires Git. It supports custom sandbox providers, plus an optional mode that runs agents directly on the host without container isolation.