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LangSmith environment variables setup

Q: LangSmith environment variables setup

Set the LANGCHAIN_TRACING_V2 environment variable to "true" to enable LangSmith tracing. Also set LANGCHAIN_API_KEY with your LangSmith API key and optionally LANGCHAIN_PROJECT to specify your project name. These variables enable automatic tracing of LangChain calls and LangSmith SDK usage.

Quick answer

Set the LANGCHAIN_TRACING_V2 environment variable to "true" to enable LangSmith tracing. Also set LANGCHAIN_API_KEY with your LangSmith API key and optionally LANGCHAIN_PROJECT to specify your project name. These variables enable automatic tracing of LangChain calls and LangSmith SDK usage.

PREREQUISITES

Python 3.8+
LangSmith API key
pip install langsmith

Setup

Install the LangSmith Python SDK and set the required environment variables to enable tracing and authentication.

bash

pip install langsmith

Step by step

Set the environment variables in your shell or Python environment before running your LangChain or LangSmith code.

LANGCHAIN_TRACING_V2=true enables LangSmith tracing.
LANGCHAIN_API_KEY holds your LangSmith API key.
LANGCHAIN_PROJECT (optional) specifies the project name for organizing traces.

Example Python code to verify environment variables and initialize LangSmith client:

python

import os
from langsmith import Client

# Verify environment variables
print("Tracing enabled:", os.environ.get("LANGCHAIN_TRACING_V2"))
print("API key set:", bool(os.environ.get("LANGCHAIN_API_KEY")))
print("Project name:", os.environ.get("LANGCHAIN_PROJECT"))

# Initialize LangSmith client
client = Client(api_key=os.environ["LANGCHAIN_API_KEY"])

# Example usage: simple traceable function
@client.traceable
def greet(name: str) -> str:
    return f"Hello, {name}!"

print(greet("World"))

output

Tracing enabled: true
API key set: True
Project name: my-project
Hello, World!

Common variations

You can set environment variables in different ways depending on your environment:

In Unix/Linux/macOS shell:
export LANGCHAIN_TRACING_V2=true
export LANGCHAIN_API_KEY=your_api_key
export LANGCHAIN_PROJECT=my-project
In Windows PowerShell:
$env:LANGCHAIN_TRACING_V2 = "true"
$env:LANGCHAIN_API_KEY = "your_api_key"
$env:LANGCHAIN_PROJECT = "my-project"
Set variables programmatically in Python before imports:
import os
os.environ["LANGCHAIN_TRACING_V2"] = "true"
os.environ["LANGCHAIN_API_KEY"] = "your_api_key"

LangSmith tracing works automatically with LangChain after setting these variables.

Troubleshooting

If tracing does not appear, verify LANGCHAIN_TRACING_V2 is set to true exactly.
If authentication fails, confirm LANGCHAIN_API_KEY is correct and has no extra spaces.
Check that environment variables are set in the same context where your Python process runs.
Restart your IDE or terminal after setting environment variables to ensure they are loaded.

✅

Key Takeaways

Set LANGCHAIN_TRACING_V2=true to enable LangSmith tracing.
Always provide LANGCHAIN_API_KEY for authentication.
Optionally set LANGCHAIN_PROJECT to organize traces by project.
Environment variables must be set in the runtime environment before execution.
LangSmith SDK uses these variables for automatic LangChain call tracing.

Verified 2026-04

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