OpenCastle
open source / 2026 - now
Open-source CLI that gives a team one shared, policy-checked configuration for seven AI coding assistants
Goal of the project
To make AI coding assistants a dependable part of how a team ships, rather than a personal trick. Every assistant reads its own config format, so a team's instructions end up scattered across several files that say almost the same thing and drift apart.
Description of the solution
OpenCastle is an open-source CLI written in TypeScript, published on npm under the MIT licence. A team writes its AI assistant config once (instructions, agents, skills, commands and MCP servers) and OpenCastle compiles it for Claude Code, GitHub Copilot, Cursor, Windsurf, OpenCode, Codex and Antigravity.
It treats that config as part of the engineering standard:
- shared baselines published as npm packages, so one standard reaches every repository
- a policy that can only tighten: MCP server allowlists, pinned versions, no inline credentials
- a lock file and a CI check that fails the pull request when generated config drifts from its source
My work on this project
I created OpenCastle and have maintained it since February 2026. The source, with 2,000+ automated tests, is on GitHub.