litelitellm 0.1.3

Lightweight Anthropic Messages API proxy with LiteLLM-style config — load your middleware from any project

litelitellm

A small, easy-to-run proxy for LiteLLM local development. No LiteLLM stack, no database — just a small FastAPI server that reads a LiteLLM-style config and loads your project’s middleware from the current directory using the same callbacks that LiteLLM provides. Optional Langfuse observability is built in.

Use it when you want the same callback/middleware contract as LiteLLM without running the full proxy. Run it from any repo via uvx.

Quick start

From a project that has a config and middleware:

1. In your project, add a config file (same format as LiteLLM):

   config.yaml (or proxy_config.yaml, or set LITELITELLM_CONFIG / LITELLM_CONFIG_PATH):

   litellm_settings:
     callbacks: ["my_middleware_loader"]
   

2. Ensure your project has a Python file my_middleware_loader.py (or whatever name you put in callbacks) that exports an object with an async_pre_call_hook method (LiteLLM CustomLogger-style).

3. From your project directory:

   uvx litelitellm
   

   Set ANTHROPIC_API_KEY (env or .env). Then point your client at the proxy, e.g.:

   ANTHROPIC_BASE_URL=http://localhost:4000 claude
   

From this repo (no middleware):

uv sync
cp .env.example .env   # set ANTHROPIC_API_KEY
uv run python -m litelitellm

Runs as passthrough only (no config callbacks in this repo).

Local testing (before PyPI): From another folder you can run the GitHub version with uvx --from git+https://github.com/elliottcarlson/litelitellm litelitellm. For editable local dev (use your local code when you run litelitellm from any folder): run uv tool uninstall litelitellm (removes the PyPI-installed tool), then from this repo run uv tool install --editable .. After that, litelitellm uses your local code. When done, uv tool uninstall litelitellm and reinstall from PyPI if you like. Alternative: from this repo run uv run litelitellm (or uv run python -m litelitellm) to always run local code without touching the global tool.

Example: instruction-injection middleware

Here’s a minimal project that injects an instruction so the model always responds like a pirate.

1. Project layout

my_project/
  config.yaml
  pirate_middleware.py
  .env          # ANTHROPIC_API_KEY=sk-ant-...

2. config.yaml

litellm_settings:
  callbacks: ["pirate_middleware"]

3. pirate_middleware.py

The middleware must expose an object with async_pre_call_hook(user_api_key_dict, cache, data, call_type). It receives the request data (e.g. model, messages, system, max_tokens) and returns the modified body.

class PirateMiddleware:
    async def async_pre_call_hook(self, user_api_key_dict, cache, data, call_type):
        # Inject a system instruction so the model responds like a pirate
        prefix = "You are a pirate. Respond only in pirate speak, with 'arr' and nautical terms. "
        existing = data.get("system")
        if existing is None:
            data["system"] = prefix.strip()
        elif isinstance(existing, str):
            data["system"] = prefix + existing
        else:
            # Anthropic can send system as a list of content blocks
            data["system"] = [{"type": "text", "text": prefix}] + list(existing)
        return data

middleware = PirateMiddleware()

4. Run

cd my_project
uvx litelitellm

Then point your client at http://localhost:4000 (e.g. ANTHROPIC_BASE_URL=http://localhost:4000). Every request will get the pirate instruction applied before being sent to the API.

Config

Config is read from the directory you run from (your project). This repo does not ship a config.

• Config path: LITELITELLM_CONFIG or LITELLM_CONFIG_PATH, then ./config.yaml, ./config.yml, ./proxy_config.yaml, or ./litellm_config.yaml.
• Callbacks: litellm_settings.callbacks — list of strings. Each entry is a module name (e.g. my_middleware_loader) or module.attribute. The module is loaded from the directory containing the config file (project root when you run from the project). The first callback that has async_pre_call_hook is used as the middleware.

Environment

Variable	Default	Description
ANTHROPIC_API_KEY	(none)	Used for outbound requests when middleware modifies the body.
LITELITELLM_HOST	0.0.0.0	Host to bind the proxy to.
LITELITELLM_PORT	4000	Port the proxy listens on.
ANTHROPIC_API_URL	https://api.anthropic.com	Upstream API.
LANGFUSE_PUBLIC_KEY	(none)	With LANGFUSE_SECRET_KEY, send traces to Langfuse.
LANGFUSE_SECRET_KEY	(none)	Langfuse secret key.
LANGFUSE_BASE_URL	https://cloud.langfuse.com	Langfuse server (e.g. http://localhost:3000 for self-hosted).

Observability

• One JSON line per request to stdout (latency, tokens, etc.).
• Optional Langfuse: set LANGFUSE_PUBLIC_KEY and LANGFUSE_SECRET_KEY (env or .env); if both are set, the proxy sends traces to Langfuse. No extra install. See LANGFUSE.md for setup with Langfuse Cloud or a self-hosted instance.

Publishing (maintainers)

• Manual: Bump version in pyproject.toml, then run uv build and uv publish (set UV_PUBLISH_TOKEN or use uv publish and enter token when prompted).
• GitHub Action: The Publish to PyPI workflow is manually triggerable (Actions → Publish to PyPI → Run workflow). Add a repository secret PYPI_API_TOKEN with your PyPI API token (pypi.org → Account → API tokens).

License

MIT. See LICENSE.