Preprints

Under Review

Agents Trust Tools Too Much: Measuring Reliance on Unreliable Tools

Hoyeol Yang*, Woojung Song*, Taewon Kim, Jonghyun Song, Seoyeon Park, Yohan Jo  Co-first

Tool-using agents are usually evaluated as if their tools always return the truth. We corrupt what web search, sub-agent delegation, and code execution return, and find that fourteen LLMs adopt the corrupted content at high rates, up to 68% for web search. Reasoning traces show agents often notice the conflict and recover the right answer internally, yet still report only the corrupted one, and none of our prompting, metadata, or post-training interventions fixes this across the board.

Web-search evaluation design

Conferences & Journals

EMNLP 2026Main

ArcANE: Do Role-Playing Language Agents Stay in Character at the Right Time?

Woojung Song*, Nalim Kim*, Sangjun Song, Chaewon Heo, Jongwon Lim, Yohan Jo  Co-first

Role-playing agents should evolve with their character, not hold a fixed persona. ArcANE, an automatically built benchmark of 17 novels and 80 characters, shows that conditioning on a Character Arc, the narrative segmented into psychological phases, outperforms every other context strategy, most of all on scenarios the source text never explores.

ArcANE construction pipeline

EMNLP 2026Main

Human Psychometric Questionnaires Mischaracterize LLM Behavior

Woojung Song*, Dongmin Choi*, Yoonah Park, Jongwook Han, Eun-Ju Lee, Yohan Jo  Co-first

The psychological profile an LLM reports on a questionnaire is not the one it shows when actually generating text. Familiar questionnaire items cue socially desirable answers, and persona effects that appear on questionnaires vanish on realistic user queries. We argue models should be profiled by what they generate, not what they self-report.

Questionnaire vs generation behavior

ACL 2026Main

Don't Adapt Small Language Models for Tools; Adapt Tool Schemas to the Models

Jonggeun Lee*, Woojung Song*, Jongwook Han, Haesung Pyun, Yohan Jo  Co-first

Small models often hallucinate tool names that follow their pretraining conventions rather than the schema they were given. PA-Tool flips the fix: instead of retraining the model, it renames schema components into naming the model already knows, cutting such errors by 80% and raising tool-use accuracy by up to 17%.

PA-Tool overview

ICLR 2026

Non-Collaborative User Simulators for Tool Agents

Jeonghoon Shim, Woojung Song, Cheyon Jin, Seungwon Kook, Yohan Jo

A user simulator that behaves like real users at their worst: asking for the unavailable, digressing, growing impatient, and leaving information out. Facing these users on MultiWOZ and τ-bench, state-of-the-art tool agents degrade sharply, hallucinating more and breaking down mid-dialogue.

Non-collaborative user simulator

TACL 2026

Psychometric Item Validation Using Virtual Respondents with Trait-Response Mediators

Sungjib Lim, Woojung Song, Eun-Ju Lee, Yohan Jo

Checking whether a survey item truly measures its intended trait normally takes costly human data collection. We instead simulate virtual respondents with LLMs, varying the mediators through which one trait can yield different answers, and keep only items that measure the trait robustly, as validated on Big Five, Schwartz values, and VIA character strengths.

Virtual respondents framework

EACL 2026Findings

Quantifying Data Contamination in Psychometric Evaluations of LLMs

Jongwook Han*, Woojung Song*, Jonggeun Lee*, Yohan Jo  Co-first

How contaminated are psychometric tests of LLMs? We measure item memorization, evaluation memorization, and target score matching across 21 models, and find that popular inventories like BFI-44 and PVQ-40 are heavily contaminated: models can even steer their answers to hit a requested score.

ACL 2025Main

Value Portrait: Assessing Language Models' Values through Psychometrically and Ecologically Valid Items

Jongwook Han*, Dongmin Choi*, Woojung Song*, Eun-Ju Lee, Yohan Jo  Co-first

A value benchmark built from real user-LLM interactions, with every item psychometrically validated against human raters' own value scores rather than annotator intuition. Across 44 LLMs, models consistently favor Benevolence, Security, and Self-Direction over Tradition, Power, and Achievement.

Value Portrait framework

PeerJ CS 2026

Interpretable Prediction of Private Brand Purchases by Pet Type in E-Commerce for Consumer Behavior Analysis Using Real-World Transaction Data

Jaehyuk Lee*, Woojung Song*, Jina Kim, Yoona Chung, Eunchan Kim  Co-first

Predicts private-brand purchases on a pet e-commerce platform from real transaction data, using per-segment XGBoost models (F1 ≈ 0.78) explained with SHAP: dog owners respond to delivery convenience, while cat owners are more price-sensitive.