Modernizing complex legacy code with AI agents | Mistral

This post details the application of AI agents for modernizing complex legacy code, specifically migrating 40,000 lines of Fortran 77 to C++. It introduces a structured workflow involving a parity harness for numerical verification, AI agents for documentation generation and code translation, and human oversight for review and unblocking agent stalls. Key technical contributions include the development of a parity harness that instruments Fortran to dump state snapshots and uses a C++ test framework for verification, the use of Vibe CLI and Mistral OCR to document scattered legacy code, and a structured agent workflow (planner, coder, tester, reviewer) with human checkpoints to ensure high-quality, maintainable code. The post highlights the importance of numerical agreement, organized documentation, and structured workflows with human review gates for large-scale legacy migrations.