langchain-ai Fetching LangSmith Traces
Requires langsmith-fetch in project dependencies and LANGSMITH_API_KEY in a .env file.
Setup
First, find the .env file containing LANGSMITH_API_KEY:
find . -name ".env" -type f 2>/dev/null | head -5
Commands
Use --env-file <path-to-.env> with all commands:
# Fetch recent traces (uses LANGSMITH_PROJECT from .env, or specify --project-uuid)
uv run --env-file <path> langsmith-fetch traces ./traces --limit 10
uv run --env-file <path> langsmith-fetch traces ./traces --project-uuid <uuid> --limit 10
# Fetch single trace by ID
uv run --env-file <path> langsmith-fetch trace <trace-id>
# Include metadata (timing, tokens, costs)
uv run --env-file <path> langsmith-fetch trace <trace-id> --include-metadata
Output Formats
--format pretty- Human-readable (default)--format json- Pretty-printed JSON--format raw- Compact JSON for piping
Troubleshooting Workflow
- Find
.env:find . -name ".env" -type f 2>/dev/null - Fetch recent traces:
uv run --env-file <path> langsmith-fetch traces ./debug --limit 10 - Find relevant trace in saved JSON files
- Check: What tools were called? What did they return? Was it correct/expected?