Legacy Code Modernizer

Legacy Code Modernizer helps you understand old code before you rewrite it. The prompt asks the model to explain what the legacy implementation does, identify technical debt, and suggest a safer modern version. It is especially useful when code contains outdated patterns, nested conditionals, manual resource handling, or brittle abstractions. Rather than jumping straight to a rewrite, the template makes the model explain the current behavior first so you can preserve intent.

This template is designed for staff engineers, modernization teams, and maintainers inheriting older systems. It emphasizes refactor planning, compatibility risks, and incremental improvements. The output can separate must-keep behavior from optional cleanup, which helps teams modernize without breaking production. It also gives you a migration path, not just a prettier code sample, so the work can be staged safely across sprints.

Customize by providing {{LEGACY_CODE}}, the target style or framework in {{TARGET_STYLE}}, and any compatibility constraints in {{COMPATIBILITY_RULES}}. If you need to preserve a specific API contract or database behavior, add that in {{HARD_REQUIREMENTS}}. The expected output is a behavior summary, modernization plan, and rewritten code when appropriate. Use this modernization prompt when you need to reduce risk while improving readability and maintainability.