The verdict
XGrammar appears in 1 AI-ranked category.
Default high-performance constrained engine in vLLM/SGLang/TensorRT-LLM for self-hosted LLMs, fast token-level guarantees, broad schema support, and production-grade throughput without external dependencies.
Where XGrammar falls short, per the models
- Grok Improve documentation and ease of schema definition for non-expert users compared to higher-level libraries
Top alternatives per the models: Instructor · Outlines · BAML · OpenAI Structured Outputs
Watch XGrammar
Boards re-poll weekly and the models change their minds. One short email only when XGrammar's standing moves — a rank change, a rival overtaking, or new reasoning from the models. Nothing otherwise.
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XGrammar ranks #10 for best structured output tool for llms by AI-model consensus. Put the badge in your README, docs or site — it updates automatically as the models re-rank.
[](https://modelsagree.com/best/best-llm-structured-output-tool?utm_source=badge&utm_medium=embed&utm_campaign=badge-xgrammar)<a href="https://modelsagree.com/best/best-llm-structured-output-tool?utm_source=badge&utm_medium=embed&utm_campaign=badge-xgrammar"><img src="https://modelsagree.com/badge/xgrammar.svg" alt="XGrammar — ranked #10 for Best structured output tool for LLMs by AI models on ModelsAgree" height="28"></a>Rankings are computed from what the models answer, re-polled on demand · raw reasoning shown verbatim · methodology