Monitoring Web Agents Without Internal Signals: Observable Trajectories and Key-Step Supervision

The paper introduces a method for monitoring web agents without relying on internal signals such as token logits. It proposes two observable trajectory representations—Macro features that capture cross‑step agent–environment interactions, and Micro features that assess consistency of intention, action, and expected state change via repeated black‑box queries. By labeling the first uncorrected critical error that leads to final failure as a key‑step boundary, the approach preserves valid early prefixes of failed trajectories and achieves risk prediction performance competitive with internal‑signal baselines across WebArena‑Lite and Online Mind2Web benchmarks.

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• agents
• benchmarks