From Cosmetic to Structural: A Paired Experiment on Metric-Guided Agentic Refactoring

Nadim Hagatulah, Markus Borg, Emma Söderberg

The role of coding agents is expanding beyond writing new code toward maintaining existing systems as AI teammates. Yet recent studies show that agent refactorings favor superficial, consistency-oriented edits over structural transformations needed to resolve Technical Debt (TD). We investigate if explicit static-analysis feedback closes this gap. Through the CodeScene MCP server, we give an open-source agent (gptme) access to code smell reports and CodeHealth (CH) scores (1--10, higher is better), and compare guided against unguided refactorings in a paired experiment covering $24{,}620$ single-file competitive programming solutions in C++, Java, and Python. We find that guidance shifts the agent from performing cosmetic edits toward structural operations, raising the rate of effective refactorings by $21$--$26$ percentage points. The benefit depends on initial code quality, with language-dependent break-even points at CH $4.9$--$7.1$, below where the structural transformations pushed by guidance increasingly risk regression, indicating where the agent needs more support to refactor. Guided runs also shift the failure profile toward logical test failures, introduce new coupling…