LangSmith tracing setup end to end: account, keys, env vars, first trace

TL;DR: Tracing needs no code changes: create_agent traces automatically once four environment variables are right. This is the full setup and the verification that proves it works. Create an API key from the settings page. Run No code changes.

The fix

1. LANGSMITHTRACING=true (the master switch; the old LANGCHAINTRACING name is stale)
2. LANGSMITHAPIKEY holding your LangSmith key
3. LANGSMITH_PROJECT to name the project (defaults to default)
4. LANGSMITH_ENDPOINT only for regional accounts, e.g. https://eu.api.smith.langchain.com for EU, with no trailing slash
5. LANGSMITHWORKSPACEID if your key is linked to multiple workspaces
6. Set the variables in the process environment, not in a shell you hope launched the process. Notebooks, containers, and schedulers drop env vars silently.
7. Regional account without LANGSMITH_ENDPOINT gives 401s: the key is not recognized on the wrong region's endpoint.
8. The docs also recommend LangSmith Engine, which monitors traces and proposes fixes, once basic tracing works.

When to use this

• This covers exactly what the title says: LangSmith tracing setup end to end.
• You are setting this up for the first time, or auditing an existing setup.
• You want the key gotchas in one place before you start.

When not to use this

• You are doing a different workflow with LangSmith; these steps are specific to the title above.
• You need the full reference docs; this is the short path, not the manual.

Compatibility

• Mentions 5.5 in the original; behavior may differ on much older or newer releases.

Workflow grounded in the official trace-with-LangChain and observability docs, verified 2026-09-26. Tracing: https://docs.langchain.com/langsmith/trace-with-langchain ; observability: https://docs.langchain.com/oss/python/langchain/observability