Efficient Prompt Optimisation for Legal Text Classification with Proxy Prompt Evaluator

Hyunji Lee, Kevin Chenhao Li, Matthias Grabmair, Shanshan Xu


Abstract
Prompt optimization aims to systematically refine prompts to enhance a language model’s performance on specific tasks. Fairness detection in Terms of Service (ToS) clauses is a challenging legal NLP task that demands carefully crafted prompts to ensure reliable results. However, existing prompt optimization methods are often computationally expensive due to inefficient search strategies and costly prompt candidate scoring. In this paper, we propose a framework that combines Monte Carlo Tree Search (MCTS) with a proxy prompt evaluator to more effectively explore the prompt space while reducing evaluation costs. Experiments demonstrate that our approach achieves higher classification accuracy and efficiency than baseline methods under a constrained computation budget.
Anthology ID:
2025.nllp-1.18
Volume:
Proceedings of the Natural Legal Language Processing Workshop 2025
Month:
November
Year:
2025
Address:
Suzhou, China
Editors:
Nikolaos Aletras, Ilias Chalkidis, Leslie Barrett, Cătălina Goanță, Daniel Preoțiuc-Pietro, Gerasimos Spanakis
Venues:
NLLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
281–290
Language:
URL:
https://preview.aclanthology.org/ingest-emnlp/2025.nllp-1.18/
DOI:
Bibkey:
Cite (ACL):
Hyunji Lee, Kevin Chenhao Li, Matthias Grabmair, and Shanshan Xu. 2025. Efficient Prompt Optimisation for Legal Text Classification with Proxy Prompt Evaluator. In Proceedings of the Natural Legal Language Processing Workshop 2025, pages 281–290, Suzhou, China. Association for Computational Linguistics.
Cite (Informal):
Efficient Prompt Optimisation for Legal Text Classification with Proxy Prompt Evaluator (Lee et al., NLLP 2025)
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PDF:
https://preview.aclanthology.org/ingest-emnlp/2025.nllp-1.18.pdf