Langfuse SDK

NOTE: This is an unofficial Langfuse SDK client for Elixir, developed and maintained by Workera.

Langfuse is an open-source platform that helps teams efficiently debug, analyze, and optimize large language model (LLM) applications by providing detailed execution insights. You can read the API documentation over here: https://api.reference.langfuse.com/.

Installation

Add Langfuse to your mix.exs dependencies:

def deps do
  [
    {:langfuse_sdk, "> 0.0"}
  ]
end

Fetch the dependency with:

mix deps.get

Configuration

In your config/config.exs, set the following:

config :langfuse_sdk,
  host: System.get_env("LANGFUSE_HOST"),
  secret_key: System.get_env("LANGFUSE_SECRET_KEY"),
  public_key: System.get_env("LANGFUSE_PUBLIC_KEY"),

You can find the secret and public key in the organizations setting in Langfuse.

Usage

Pseudo-code that shows how to start create traces in Langfuse.

defmodule MyApp do
  alias LangfuseSdk.Tracing.Generation
  alias LangfuseSdk.Tracing.Event
  alias LangfuseSdk.Tracing.Trace
  
  def start_listener(context) do
    # Create a langfuse event
    trace = Trace.new(%{
      name: "my-trace",
      id: "unique-id",
      user_id: context.user_id,
      metadata: %{}
    })

    {:ok, data} = LangfuseSdk.create(trace)
  end

  def received_event(event, context) do
    # Create a Langfuse event
    %{name: event.name, trace_id: context.trace_id}
    |> Event.new()
    |> LangfuseSdk.create()

    open_ai_call_with_traces(event, context)
  end

  defp open_ai_call_with_traces(event, context) do
    # Create a langfuse observation
    generation =
      Generation.new(%{
        name: context.generation_name,
        input: event.data,
        trace_id: context.trace_id,
        model: context.model,
        metadata: %{response_format: context.response_format},
        completion_start_time: DateTime.utc_now()
      })

    LangfuseSdk.create(generation)

    # Execute the OpenAI call
    response = OpenAIClient.chat_completion(
      model: context.model,
      messages: event.data,
      response_format: context.response_format)

    # Update the Langfuse trace with the result
    LangfuseSdk.update(%{
      generation
      | end_time: DateTime.utc_now(), output: %{role: "assistant", output: parse_output(response)}
    })

    :ok
  end
end

Development

OpenAPI code generation and syncing

Langfuse APIs are following the OpenAPI specifications, which has been used to generate the SDK code using the open-api-generator library. The generated code lives inside the generated folder.

Running this command is only recommended to update the generate code because it may introduce incompatibilities in the current API implementation.

Run mix sdk.build to regenerete the API. This command will download the latest version of the OpenAPI YAML specification and generate the correspondent code to match the API spec.

Contributing

Contributions are welcome! Fork the repo and submit a pull request. For major changes, open an issue to discuss them first.

License

MIT License. See the LICENSE file for details.