TL;DR

API-Bank is the first comprehensive benchmark for tool-augmented LLMs, covering 73 runnable APIs across three skill dimensions — planning, retrieval, and execution — with a fine-tuned Lynx model surpassing Alpaca by over 26 points.

Summary

Tool-augmented LLMs must plan which APIs to call, retrieve them from a catalog, and execute calls correctly — yet no systematic benchmark existed for this three-stage pipeline. API-Bank provides 73 runnable API tools, 314 annotated dialogues with 753 API calls, and a 1,888-dialogue training set spanning 2,138 APIs across 1,000 domains. GPT-4 excels at planning while GPT-3.5 leads on retrieval. Fine-tuning Alpaca on the training set produces Lynx, which surpasses the base model by over 26 percentage points and approaches GPT-3.5 performance.

Key contributions

  1. Introduces API-Bank, the first benchmark decomposing tool use into three evaluable skills: planning, retrieval, and API call execution.
  2. Provides 73 runnable tools with ground-truth API calls, enabling execution-level evaluation beyond text matching.
  3. Shows that GPT-4 and GPT-3.5 specialize differently — no single model dominates all three tool-use dimensions.
  4. Produces Lynx via fine-tuning, demonstrating that a 1,000-domain training set enables smaller models to approach GPT-3.5.
  5. Identifies multi-step API chaining as the hardest unsolved subproblem for production tool-augmented systems.

When to cite

  1. When evaluating or benchmarking LLM tool use across the planning, retrieval, and execution dimensions.
  2. When arguing that planning and retrieval are separable skills that should be improved independently.
  3. When citing evidence that fine-tuning on tool-use data enables smaller models to approach large-model performance.
  4. When discussing the difficulty of multi-step API chaining and error recovery in agentic LLM systems.

LLM Generative AI Prompt Engineering ART - Automatic multi-step reasoning and tool-use for large language models An LLM Compiler for Parallel Function Calling