At a high level, you will define your AI prompts and interfaces in BAML files. The BAML compiler will then generate Python or Typescript code for you to use in your application, depending on the generators configured in your main.baml:

generator MyGenerator{
  language "python"
  // This is where the generated baml-client will be written to
  project_root "../"
  test_command "poetry run python -m pytest"
  install_command "poetry add baml@latest"
  package_version_command "poetry show baml"

Here is the typical project structure:

├── baml_client/ # Generated code
├── baml_src/ # Prompts live here
│   ├── __tests__/ # Tests loaded by playground
│   │   └── YourAIFunction/
│   │       └── test_1.json
│   ├── main.baml
│   ├── any_directory/
│   │   └── baz.baml
│   └── foo.baml
# The rest of your project (not generated nor used by BAML)
├── app/
│  ├──
│  └──
├── pyproject.toml
└── poetry.lock

  1. baml_src/ is where you write your BAML files with the AI function declarations, prompts, retry policies, etc. It also contains generator blocks which configure how and where to transpile your BAML code.

  2. baml_client/ is where the BAML compiler will generate code for you, based on the types and functions you define in your BAML code.

from baml_client import baml as b

async def use_llm_for_task():
  await b.CallMyLLM()
  1. baml_src/__tests__/**/*.json is where your test inputs live. The VSCode extension allows you to load, delete, create, and run any of these these inputs. You can also use these tests ou like. See here for more information.

You should never edit any files inside baml_client directory as the whole directory gets regenerated on every baml build (auto runs on save if using the VSCode extension).

If you ever run into any issues with the generated code (like merge conflicts), you can always delete the baml_client directory and it will get regenerated automatically once you fix any other conflicts in your .baml files.


BAML by default has global imports. Every entity declared in any .baml file is available to all other .baml files under the same baml_src directory. You can have multiple baml_src directories, but no promises on how the VSCode extension will behave (yet).