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What is BAML?

BAML is a domain-specific language to write and test LLM functions.

In BAML, prompts are treated like functions. An LLM function is a prompt template with some defined input variables, and a specific output type like a class, enum, union, optional string, etc.

With BAML you can write and test a complex LLM function in 1/10 of the time it takes to setup a python LLM testing environment.

Try it out in the playground —

Share your creations and ask questions in our Discord.

Demo video


Language features

  • Python / Typescript / Ruby support: Plug-and-play BAML with other languages
  • JSON correction: BAML fixes bad JSON returned by LLMs (e.g. unquoted keys, newlines, comments, extra quotes, and more)
  • Wide model support: Ollama, Openai, Anthropic, Gemini. Tested on small models like Llama2
  • Streaming: Stream structured partial outputs
  • Resilience and fallback features: Add retries, redundancy, to your LLM calls

Developer Experience

  • Stability: BAML works the same in EVERY language we support. No more “it works in python but not in Typescript”
  • Type safety: BAML is a typed language, so you get type errors before you run your LLM, and autocomplete in your IDE
  • Realtime Prompt Previews: See the full prompt always, even if it has loops and conditionals
  • Testing support: Test functions in the playground with 1 click

Production features

  • Observability Platform: Use Boundary Studio to visualize your functions and replay production requests with 1 click

Companies using BAML

  • Zenfetch - ChatGPT for your bookmarks
  • Vetrec - AI-powered Clinical Notes for Veterinarians
  • MagnaPlay - Production-quality machine translation for games
  • Aer Compliance - AI-powered compliance tasks
  • Haven - Automate Tenant communications with AI
  • Muckrock - FOIA request tracking and filing
  • and more! Let us know if you want to be showcased or want to work with us 1-1 to solve your usecase.

Starter projects

First steps

We recommend checking the examples in Once you’re ready to start, install the toolchain and read the guides.