Application Refactoring

Refactoring is changing the internal structure of code without changing its observable behavior, in small steps backed by tests, to make it easier to understand and change.

Refactoring improves code structure, while re-architecting changes the architecture of an application, for example splitting a monolith into services. Modernization programs often do both. See the Application Modernization page.

Usually incrementally: identify boundaries, route traffic through a facade, extract one capability at a time and retire the old code, a technique known as the strangler fig pattern. See the pattern pages from Fowler, AWS and Azure, and the Microservices Architecture Tools page.

They apply code changes programmatically, for example OpenRewrite recipes for Java, Rector for PHP, jscodeshift for JavaScript and LibCST for Python, so the same change can be made across many files or repositories. AI coding agents can also perform refactors, which need review and tests.

Tests that pin down existing behavior make refactoring much safer. For legacy code without tests, teams often add characterization tests first. See the Software Quality and CI/CD Tools pages.

Replatforming moves an application to a new runtime or managed service with limited code change, while refactoring changes the code or architecture itself. See the Replatforming page.

Links and release facts were checked on 31 October 2026 from GitHub and PyPI. jscodeshift's latest release is from March 2025 and Comby's from June 2022, as their cards note. Descriptions follow each source's own pages and are not rankings.