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

1. Find .env: find . -name ".env" -type f 2>/dev/null
2. Fetch recent traces: uv run --env-file <path> langsmith-fetch traces ./debug --limit 10
3. Find relevant trace in saved JSON files
4. Check: What tools were called? What did they return? Was it correct/expected?