CPJudgeBench: Meta-Evaluation of LLM Judges for Constraint Programming through Solution-Space Semantics

Nastaran Moradzadeh Farid, Alireza Taghizadeh, Tommaso Di Noia, Yashar Deldjoo, Sara Shafiee


Abstract
Large Language Models (LLMs) are increasingly used as evaluators for code generation, but existing judge benchmarks mainly target general-purpose programming. Constraint Programming (CP) requires a stricter notion of correctness: a model is correct only if it faithfully represents the intended solution space, not merely if it executes, preserves satisfiability, or returns one valid solution. We introduce CPJudgeBench, a benchmark for meta-evaluating LLM judges of CP modeling correctness through solver-supported solution-space semantics. It contains 522 solver-validated candidate models from 82 CP problem families in CPMpy and MiniZinc, labeled as equivalent, unsound, incomplete, mixed, or non-executable. Across our experiments, we meta-evaluate a total of 15 LLM judges through semantic-label, binary-correctness, and score-based protocols. Results show that fine-grained semantic judging remains difficult, especially for reference-free MiniZinc, while stronger reasoning- and code-oriented models perform more reliably. Score-based LLM judgments also align better with solution-space similarity than standard text or code metrics. The benchmark system is available at https://github.com/Nastaran95/CPJudgeBench.
Anthology ID:
2026.emnlp-main.1648
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
37459–37478
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URL:
https://aclanthology.org/2026.emnlp-main.1648/
DOI:
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Cite (ACL):
Nastaran Moradzadeh Farid, Alireza Taghizadeh, Tommaso Di Noia, Yashar Deldjoo, and Sara Shafiee. 2026. CPJudgeBench: Meta-Evaluation of LLM Judges for Constraint Programming through Solution-Space Semantics. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 37459–37478, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
CPJudgeBench: Meta-Evaluation of LLM Judges for Constraint Programming through Solution-Space Semantics (Farid et al., EMNLP 2026)
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https://aclanthology.org/2026.emnlp-main.1648.pdf