Instruction-Following Evaluation in Function Calling for Large Language Models
Existing function-calling evaluation benchmarks (e.g., BFCL, tau²-Bench) assess only parameter semantic correctness, neglecting models’ adherence to syntactic formatting instructions—such as quoted strings or ISO date formats. Method: We introduce the first benchmark explicitly targeting *format instruction adherence*, comprising 750 test cases with explicit, diverse formatting constraints. Leveraging embedded JSON Schema validation rules, our benchmark enables fully automated, algorithmic evaluation. Contribution/Results: It is the first to systematically quantify large language models’ precision in executing embedded formatting directives within structured outputs. Experiments reveal alarmingly high error rates—30%–60%—even for state-of-the-art models (e.g., GPT-5, Claude 4.1 Opus) on basic formatting requirements, exposing a critical reliability gap for AI agents in real-world deployment.