Trace Every Cursor Agent Turn in LangSmith
Summary
This walkthrough details how to integrate LangSmith tracing with Cursor agents, ensuring that every agent turn is captured as a full, inspectable trace in LangSmith. The process involves installing the LangSmith plugin in Cursor, setting three specific environment variables (including `LANGCHAIN_TRACING_V2`), and running an end-to-end task to verify the hook's functionality.
Key takeaways
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Full Trace Capture
By implementing this setup, every agent turn executed by Cursor is logged as a distinct trace in LangSmith, providing comprehensive visibility into the agent's execution flow.
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Trace Structure Details
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Each trace captures the model run details (model name, token usage), input/output, tool runs (e.g., file reads, shell commands), and nested tasks if sub-agents are involved.
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Cross-Agent Comparison
LangSmith maintains a common trace structure that allows users to compare traces from multiple agents (Cursor, Claude Code, and Codex) within the same workspace.
Technical details
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Prerequisites & Installation
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Requires Cursor and Node.js. The LangSmith plugin is installed by pasting the provided repo URL into the Cursor settings > plugins field.
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Environment Variables
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Three environment variables must be set in the shell config: `LANGCHAIN_TRACING_V2` (enables tracing), an API key for authentication, and `LANGCHAIN_API_STRATEGY` (or similar product name variable) to define where traces land.
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Verification
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The hook's functionality is confirmed by tailing the log file with a specific command and observing activity after running a Cursor agent task.
Mentioned resources
Channel & topics
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