Study: Code Cleanliness Doesn't Affect Coding Agent Success Rates but Reduces Token Usage by 8% and File Revisits by 34%

Code cleanliness does not change the agent's pass rate. However, it substantially alters the agent's operational footprint: agents working on cleaner code use 7 to 8% fewer tokens and reduce file revisitations by 34%.

Our findings suggest that traditional maintainability principles remain highly relevant in the era of AI-driven development, shaping the computational cost and navigational efficiency of coding agents.

Code cleanliness joins model choice, harness, and prompting as a factor that materially affects agent behaviours.

To isolate the effect of code cleanliness from agent capability, we introduce an evaluation protocol built around minimal pairs: repositories that match on architecture, dependencies, and external behaviour, but differ on static-analysis rule violations and cognitive complexity.