API Circle Studio is a Git-backed, AI-native API workspace for developers. Build collections, environments, mocks, assertions, and execution plans across Desktop, Web, VS Code, CLI, and MCP. Workspaces live as JSON you can diff, review, and sync through Git — while Claude, Cursor, Copilot, and ChatGPT can read, author, and run requests through MCP. Source-available, local-first, and built for API teams that want ownership.