Hopper is the first agentic development environment for mainframe and COBOL. It allows AI agents to navigate TN3270, inspect datasets, write JCL, debug jobs, query VSAM, and operate inside z/OS from a modern development environment. Combines a real mainframe terminal, context panels for datasets and jobs, and an AI agent that safely operates across TN3270, ISPF, JCL, JES, CICS, VSAM, and spool output.