LangSmith

At a glance

Availability: Experimental (how to enable).
Auth: API key.
Connection: The key from LANGSMITH_API_KEY is sent as the x-api-key header.
Docs: https://docs.langchain.com/langsmith/create-account-api-key

Set these per environment. See Connect an integration.

Variable	Required	Description
`LANGSMITH_API_KEY`	Yes	LangSmith API key (starts with lsv2_) Docs.

Create a LangSmith account: Sign up at https://smith.langchain.com - the free Developer plan includes traces for testing.
Create an API key: In LangSmith go to Settings → API Keys and create a key (Personal Access Token or Service Key). Copy it immediately - it is only shown once.
Store the key: Add it to your .env file as LANGSMITH_API_KEY=lsv2_…
Verify access: Run the List Projects tool. If you belong to multiple workspaces, make sure the key was created in the workspace you want to query.

API keys are workspace-scoped; data from other workspaces is not visible to the key
EU-region organizations use https://eu.api.smith.langchain.com - these tools target the default US endpoint
Query Runs filter expressions are documented at https://docs.langchain.com/langsmith/trace-query-syntax

Tool	Access	Description
List Projects	Read	List tracing projects (tracer sessions) in your LangSmith workspace
Query Runs	Read	Query traced runs with filters (project, trace filter expressions, root runs only)
Get Run	Read	Get full details of a single run, including inputs, outputs, and errors
List Datasets	Read	List evaluation datasets in your LangSmith workspace
List Examples	Read	List examples in a LangSmith dataset

Query my LangSmith projects for recent runs with errors and summarize what went wrong.
List my LangSmith tracing projects with their run counts and last activity.