Do Coding Agents Still Need a Debugger? Frontier-Model-Based Fault Localization at the Accuracy Ceiling

The study evaluates frontier large language models—Sol 6.1, Luna 6, and Qwen 3.8—in their ability to localize faults in LeetCode solutions without tools, with optional debugger assistance, or with encouraged debugger use. Across 610 seeded single‑line faults and five behavior‑preserving transformations, the agents achieved 98.2–99.9% accuracy on original code and 96.7–99.9% on transformed code when no tools were used. Encouraged debugger assistance further improved Luna 6 and Qwen 3.8’s accuracy by 61–63% of remaining errors, albeit at a 14.7–27.0× increase in token usage, while Sol 6.1 maintained 99.9% accuracy regardless of debugger use.

Machine-generated by The Flow from the publisher's headline and feed description — not written or checked by a human. The full article lives at arXiv AI.

• llms
• agents