Fix Langfuse API key error
public_key or secret_key is missing or incorrectly set during client initialization. Ensure you provide both keys explicitly from os.environ when creating the Langfuse instance to fix authentication failures.config_error public_key and secret_key from environment variables when initializing Langfuse to resolve API key errors.Why this happens
Langfuse requires two distinct API keys: a public_key and a secret_key. A common mistake is to provide only one key or to misname the environment variables. This leads to authentication errors or failures when making API calls.
Typical error output includes authentication failures or exceptions indicating missing credentials.
Example of incorrect initialization:
from langfuse import Langfuse
import os
# Incorrect: only one key provided
langfuse = Langfuse(public_key=os.environ["LANGFUSE_API_KEY"])
# This will raise an error because secret_key is missingTypeError: __init__() missing 1 required positional argument: 'secret_key'
The fix
Provide both public_key and secret_key explicitly from environment variables when initializing the Langfuse client. This ensures proper authentication and prevents API key errors.
Correct code example:
from langfuse import Langfuse
import os
langfuse = Langfuse(
public_key=os.environ["LANGFUSE_PUBLIC_KEY"],
secret_key=os.environ["LANGFUSE_SECRET_KEY"],
host="https://cloud.langfuse.com"
)
# Now you can safely use langfuse to observe or trace calls
@langfuse.observe()
def my_llm_call(prompt: str) -> str:
return "response"
print("Langfuse client initialized successfully.")Langfuse client initialized successfully.
Preventing it in production
Always validate that both LANGFUSE_PUBLIC_KEY and LANGFUSE_SECRET_KEY environment variables are set before starting your application. Use configuration checks or startup scripts to fail fast if keys are missing.
Implement retry logic with exponential backoff around API calls to handle transient network or auth errors gracefully.
Securely store and rotate keys regularly to maintain security compliance.
Key Takeaways
- Always provide both public_key and secret_key from environment variables when initializing Langfuse.
- Validate environment variables at app startup to avoid runtime authentication errors.
- Use exponential backoff retries to handle transient API key or network issues gracefully.