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Implement distributed tracing


This feature is currently only available in the Python SDK. Support for TypeScript is coming soon.

Sometimes, you need to trace a request across multiple services.

LangSmith supports distributed tracing out of the box, linking runs within a trace across services using context propagation headers (langsmith-trace and optional baggage for metadata/tags).

Example client-server setup:

  • Trace starts on client
  • Continues on server
from langsmith.run_helpers import get_current_run_tree, traceable
import httpx

async def my_client_function():
headers = {}
async with httpx.AsyncClient(base_url="...") as client:
if run_tree := get_current_run_tree():
# add langsmith-id to headers
return await"/my-route", headers=headers)

Then the server (or other service) can continue the trace by passing the headers in as langsmith_extra:

from langsmith import traceable
from langsmith.run_helpers import tracing_context
from fastapi import FastAPI, Request

async def my_application():

app = FastAPI() # Or Flask, Django, or any other framework"/my-route")
async def fake_route(request: Request):
# request.headers: {"langsmith-trace": "..."}
# as well as optional metadata/tags in `baggage`
with tracing_context(parent=request.headers):
return await my_application()

The example above uses the tracing_context context manager. You can also directly specify the parent run context in the langsmith_extra parameter of a method wrapped with @traceable.

from langsmith.run_helpers import traceable, trace
# ... same as above"/my-route")
async def fake_route(request: Request):
# request.headers: {"langsmith-trace": "..."}
my_application(langsmith_extra={"parent": request.headers})

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