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Let Me Speak Freely? A Study on the Impact of Format Restrictions on Performance of Large Language Models

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arxiv 2408.02442 v3 pith:RCZHANVS submitted 2024-08-05 cs.CL

classification cs.CL
keywords llmsformatperformancereasoningabilitiesconstraintsformatsgeneration
verification ladder T0 review T1 audit T2 compute T3 formal
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Structured generation, the process of producing content in standardized formats like JSON and XML, is widely utilized in real-world applications to extract key output information from large language models (LLMs). This study investigates whether such constraints on generation space impact LLMs abilities, including reasoning and domain knowledge comprehension. Specifically, we evaluate LLMs performance when restricted to adhere to structured formats versus generating free-form responses across various common tasks. Surprisingly, we observe a significant decline in LLMs reasoning abilities under format restrictions. Furthermore, we find that stricter format constraints generally lead to greater performance degradation in reasoning tasks.

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Cited by 15 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. PhantomFill: When the Form Demands an Answer, Language Models Invent One

    cs.LG 2026-06 conditional novelty 7.0 of 10

    Required JSON fields make LLMs invent answers to unanswerable questions 100% of the time in ten of thirteen models, even when an 'insufficient evidence' escape exists.

  2. Knowledge-Conditioned, Single-Pass LLM Synthesis of Executable Unity Game Scenes: A Compiler Error Census across 26 Goal Playable Concepts

    cs.LG 2026-07 accept novelty 6.5 of 10

    Single-pass LLM generation of Unity scenes for 26 Goal Playable Concepts yields zero compilable scripts; Grounding vs Hygiene errors order patterns by engine-knowledge demand.

  3. Structured Output Collapses Answer Diversity Across 44 Language Models

    cs.CL 2026-07 conditional novelty 6.0 of 10

    Requesting JSON instead of plain chat measurably reduces answer diversity across 44 LLMs, concentrating answers onto the field's modal choice.

  4. Compression, structure, and executor capability: a controlled real-cost decomposition of language-model agent skill optimisation

    cs.SE 2026-07 accept novelty 6.0 of 10

    On 40 software-engineering agent tasks, executor model tier dominates skill optimisations: no shortening, structure, scoped loading, or compiler tier beats raw skills on quality or real cost.

  5. Attributing Structured-Output Gains in Function Calling: Interface Alignment versus Procedural Transfer

    cs.SE 2026-07 accept novelty 6.0 of 10

    On BFCL and API-Bank, format-only prompts and generic procedural text often match or beat extracted skills, so many skill-injection gains are interface alignment, not procedural transfer.

  6. The Format Tax

    cs.CL 2026-04 conditional novelty 6.0 of 10

    Structured-output instructions alone impose a large accuracy tax on open-weight LLMs; decoupling freeform reasoning from formatting recovers most of it, while recent closed models largely avoid the tax.

  7. Structure Enables Effective Self-Localization of Errors in LLMs

    cs.AI 2026-02 conditional novelty 6.0 of 10

    Structuring reasoning into discrete thoughts lets LLMs find their first error and backtrack, improving self-correction by 20–40% under oracle verification and beating self-correction baselines autonomously.

  8. Scaling Truth: The Confidence Paradox in AI Fact-Checking

    cs.SI 2025-09 conditional novelty 6.0 of 10

    Across LLM fact-checking, model scale correlates with an inverse pattern of accuracy and decisiveness: smaller models are overconfident and less accurate, larger models are accurate but overly cautious.

  9. SC2Arena and StarEvolve: Benchmark and Self-Improvement Framework for LLMs in Complex Decision-Making Tasks

    cs.LG 2025-08 conditional novelty 6.0 of 10

    The authors propose SC2Arena, a full-coverage StarCraft II benchmark for LLMs, and StarEvolve, a planner-executor-verifier self-improvement framework, claiming superior strategic planning.

  10. Knowledge Conceptualization Impacts RAG Efficacy

    cs.AI 2025-07 conditional novelty 6.0 of 10

    An empirical study showing that both schema complexity and representation format affect how well GPT-4o generates SPARQL queries from competency questions, with mixed results across two knowledge graph families.

  11. Decoupling Task-Solving and Output Formatting in LLM Generation

    cs.CL 2025-10 conditional novelty 5.0 of 10

    A decoding-time method that keeps the format in a separate module improves LLM accuracy by 1–6% with guaranteed format compliance on math, judging, and extraction.

  12. Fine-tuning for Better Few Shot Prompting: An Empirical Comparison for Short Answer Grading

    cs.LG 2025-08 conditional novelty 5.0 of 10

    Fine-tuning GPT-4o-mini on about 150 examples raised short-answer grading F1 from 0.68 to 0.73; QLoRA fine-tuning of Llama 3.1 8B only reached 0.65 after adding synthetic data.

  13. REST: Stress Testing Large Reasoning Models by Asking Multiple Problems at Once

    cs.CL 2025-07 conditional novelty 5.0 of 10

    Asking a reasoning model several problems at once reveals large accuracy drops and exposes differences that single-question benchmarks miss.

  14. Leveraging LLMs for Mission Planning in Precision Agriculture

    cs.RO 2025-06 conditional novelty 5.0 of 10

    ChatGPT can generate valid behavior-tree mission plans for agricultural robots from natural-language requests, but spatial and route-optimization tasks still require an external stochastic-orienteering solver.

  15. AI Prototyper: A Figma Plugin for Decomposition-Based GUI Prototyping with LLMs

    cs.SE 2026-07 conditional novelty 4.0 of 10

    An LLM-based Figma plugin with a human-editable feature list and RAG component retrieval produced more completed prototypes and higher expert quality ratings than manual Figma in a small Thai-language pilot.

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