How to Fix LangSmith API key validation failed: unauthorized request (LangSmith)

Quick Answer: This error occurs when LangSmith rejects your API key due to incorrect credentials, expiration, or misconfigured environment variables. The fastest fix is to regenerate your API key in the LangSmith dashboard and update your local or deployment environment variables.

What Causes This Error

• The LANGSMITH_API_KEY environment variable is missing, mistyped, or outdated.
• The API key was deleted or revoked from the LangSmith platform.
• You are pointing to the wrong LangSmith endpoint or region (e.g., EU vs. US cluster).
• Environment variables are not properly loaded in your runtime environment (e.g., missing .env file or deployment secrets).

Step-by-Step Fixes

Fix 1: Fix 1: Regenerate and Update Your API Key

Log in to your LangSmith account and navigate to Settings > API Keys.,Delete the old API key and click 'Create API Key' to generate a new one.,Update your local .env file or system environment variables with export LANGSMITH_API_KEY='your-new-key'.

Fix 2: Fix 2: Verify Environment Variable Names

Check your code to ensure you are using the correct variable name: LANGSMITH_API_KEY (not LANGCHAIN_API_KEY, though older SDK versions supported both, standardizing on LANGSMITH_API_KEY is recommended).,Ensure tracing is explicitly enabled by setting LANGSMITH_TRACING=true.

Fix 3: Fix 3: Check Deployment Platform Secrets

If running on Vercel, AWS, Docker, or Render, navigate to your project's environment settings or secret manager.,Verify that LANGSMITH_API_KEY is added to the correct deployment environment (Production, Preview, Development).,Trigger a redeployment of your application after updating the secrets.

Advanced Fixes

Advanced Fix 1: Advanced: Endpoint and Region Configuration Check

If you are using LangSmith Enterprise or a specific regional cluster, verify that LANGSMITH_ENDPOINT is set correctly (e.g., https://api.smith.langchain.com).,Inspect outbound network requests using a proxy or debugging tool to ensure headers are passing 'x-api-key' or 'Authorization: Bearer' correctly.

FAQs

Q: Does LangSmith require a paid plan to use API keys?

A: No, LangSmith offers a free tier, but a valid API key generated from a registered account is always required to authenticate tracing requests.

Q: Why is my code working locally but failing in production?

A: This usually happens when the .env file is present on your local machine but the environment variables have not been explicitly added to your cloud hosting provider's dashboard.