A technical breakdown of two key mechanisms for building reliable LLM-powered agents: structured outputs and function calling. Structured outputs use grammar-constrained decoding to enforce schema compliance in a single turn, making them ideal for data extraction, query generation, and formatting tasks. Function calling enables multi-turn interactions with external tools and APIs, giving agents the ability to fetch data and execute actions dynamically. The post covers performance, latency, and cost trade-offs, and recommends a hybrid 'Controller + Formatter' pattern for production agent architectures, along with a 3-step decision tree for choosing between the two approaches.

8m read timeFrom machinelearningmastery.com
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Table of contents
IntroductionUnpacking the Mechanics: How They Work Under the HoodWhen to Choose Structured OutputsWhen to Choose Function CallingPerformance, Latency, and Cost ImplicationsHybrid Approaches and Best PracticesWrapping Up

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