AgentBack is an ESM/Zod/MCP fork of LoopBack 4 for building HTTP APIs and MCP servers from one codebase. Define a Zod schema once on a decorator and it becomes your request validation, OpenAPI 3.1 spec, MCP tool, and a codegen-free typed client — all from the same DI container. AI coding agents get a real contract to build against, so they can't drift into a second source of truth or a mismatched endpoint. Best practice becomes the path of least resistance. On npm today.