Banana (bananaml), an ML infrastructure company, created Fructose as an open-source project.

A Python library where a decorator turns type-annotated function signatures into strongly-typed LLM calls.

Installed as a Python package and used within any Python codebase calling supported LLM APIs.

Released in 2024 and available on GitHub since then.

Guarantees correctly-typed outputs, including primitives, dataclasses, enums, and nested types, without manual prompt engineering or output parsing.

Wraps calls to LLM provider APIs such as OpenAI, using function signatures rather than external schema files.

Open-source (Apache-2.0 license) on GitHub, self-hosted library, sends prompts to whichever LLM API the developer configures.