Lesson 1265 of 1596
Tool Calling Grammars: How AI Models Produce Reliable Structured Output
Constrained decoding via grammars or finite-state machines guarantees AI tool calls parse correctly.
Creators · AI Foundations · ~16 min read
The premise
Constrained decoding uses a grammar or finite-state machine to mask invalid tokens at each step. The model literally cannot produce malformed JSON or invalid tool calls.
What AI does well here
- Guarantee syntactically valid JSON, XML, or function calls
- Reduce retry loops in agentic systems substantially
- Enable smaller models to do reliable tool calling
What AI cannot do
- Make the model choose the right tool — only ensure valid syntax
- Substitute for evaluation of whether the call accomplishes the goal
- Eliminate the need for runtime validation of business rules
Key terms in this lesson
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