Langfuse | Respan Docs

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1 {
2   "mcpServers": {
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5     }
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What is Langfuse?

Langfuse is an open-source LLM observability platform. The Respan instrumentor patches Langfuse’s OTLP exporter to redirect traces to Respan — your existing @observe decorators and langfuse.trace() calls continue to work unchanged.

Check

Example project: GitHub Link

Setup

Install packages

$ pip install langfuse respan-instrumentation-langfuse

Set environment variables

$ export RESPAN_API_KEY="YOUR_RESPAN_API_KEY"
$ export LANGFUSE_PUBLIC_KEY="YOUR_LANGFUSE_PUBLIC_KEY"
$ export LANGFUSE_SECRET_KEY="YOUR_LANGFUSE_SECRET_KEY"

Instrument before importing Langfuse

LangfuseInstrumentor().instrument() must be called before importing langfuse. The instrumentor patches the OTLP exporter at import time.

1 import os
2 from respan_instrumentation_langfuse import LangfuseInstrumentor
3 
4 # Instrument BEFORE importing langfuse
5 LangfuseInstrumentor().instrument()
6 
7 # Now import and use langfuse normally
8 from langfuse.decorators import observe
9 from openai import OpenAI
10 
11 client = OpenAI()
12 
13 @observe()
14 def generate_joke():
15     response = client.chat.completions.create(
16         model="gpt-4o-mini",
17         messages=[{"role": "user", "content": "Tell me a joke about AI"}],
18     )
19     return response.choices[0].message.content
20 
21 @observe()
22 def joke_pipeline():
23     joke = generate_joke()
24     return joke
25 
26 result = joke_pipeline()
27 print(result)

View your trace

Open the Traces page to see your Langfuse traces in Respan.

Configuration

See the Langfuse Instrumentor SDK reference for the full API.