Extender: A Multi-agent System for Code Extensibility Review

Abstract

Software systems must evolve as requirements and environments change, which makes extensibility a central quality goal. The SOLID principles, five object-oriented design principles, are widely endorsed in software engineering practice to evaluate software quality. However, automatically detecting violations of SOLID principles remains difficult since many violations are latent design flaws that only surface when the code must be extended. In this paper, we propose to check the violations of SOLID principles by explicitly extending and checking the extensibility of existing code. Based on this idea, we design , a multi-agent system that detects SOLID violations by generating principle-specific extension requirements, asking AI agents to implement them, and checking whether the resulting diffs expose design defects. Experimental results show that achieves 87.9% detection accuracy with a Qwen3.5 9B model, which is 32.1 points higher than the state-of-the-art LLM-based approaches.