COBOL Build

Many organizations still depend on COBOL programs for important batch processes. Their business rules can be difficult to understand because documentation is incomplete and experienced maintainers are scarce. Rewriting a program in a newer language is risky: a small difference in rounding, record formatting, or error handling can change a financial result. COBOL Bridge is a developer workflow for making that transition easier to inspect and verify. It starts with a COBOL program and synthetic test inputs. IBM Bob 2.0 explains the program and helps identify its record layouts and business rules. The workflow runs the original program and saves its observed outputs as characterization fixtures. Those outputs become the reference for two rewrites: COBOL to Java, followed by Java to Python. An MCP server gives Bob and other compatible clients tools to inspect the source, run the programs, and compare results. The parity report identifies differences by record and field, including formatting and trailer totals. When a result differs, the developer can trace it back to the original COBOL behavior and correct the new implementation without silently changing the reference output. The prototype focuses on one synthetic batch program so the full workflow can be demonstrated clearly. Developers and QA engineers can inspect the explanation, both rewritten versions, the test cases, and the parity reports. The aim is to turn an uncertain rewrite into a series of changes whose behavior can be checked. One sample does not prove that every COBOL system can be converted automatically, but it shows a repeatable approach to safer modernization.