Harrison/tracing docs (#804)

Co-authored-by: Ankush Gola <9536492+agola11@users.noreply.github.com>
2025-09-08 14:31:55 +00:00 · 2023-01-29 20:24:22 -08:00
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+# LangChain Tracing Instructions
+
+First, you should install tracing and set up your environment properly.
+You can use either a locally hosted version of this (uses Docker) or a cloud hosted version (in closed alpha).
+
+- [Locally Hosted Setup](./tracing/local_installation.md)
+- [Cloud Hosted Setup](./tracing/hosted_installation.md)
+
+## Tracing Walkthrough
+
+When you first access the UI, you should see a page with your tracing sessions. 
+An initial one "default" should already be created for you. 
+A session is just a way to group traces together. 
+If you click on a session, it will take you to a page with no recorded traces that says "No Runs." 
+You can create a new session with the new session form.
+
+![](tracing/homepage.png)
+
+If we click on the `default` session, we can see that to start we have no traces stored.
+
+![](tracing/default_empty.png)
+
+If we now start running chains and agents with tracing enabled, we will see data show up here.
+To do so, we can run [this notebook](tracing/agent_with_tracing.ipynb) as an example.
+After running it, we will see an initial trace show up.
+
+![](tracing/first_trace.png)
+
+From here we can explore the trace at a high level by clicking on the arrow to show nested runs.
+We can keep on clicking further and further down to explore deeper and deeper.
+
+![](tracing/explore.png)
+
+We can also click on the "Explore" button of the top level run to dive even deeper. 
+Here, we can see the inputs and outputs in full, as well as all the nested traces.
+
+![](tracing/explore_trace.png)
+
+We can keep on exploring each of these nested traces in more detail.
+For example, here is the lowest level trace with the exact inputs/outputs to the LLM.
+
+![](tracing/explore_llm.png)
+
+## Changing Sessions
+1. To initially record traces to a session other than `"default"`, you can set the `LANGCHAIN_SESSION` environment variable to the name of the session you want to record to:
+
+```python
+import os
+os.environ["LANGCHAIN_HANDLER"] = "langchain"
+os.environ["LANGCHAIN_SESSION"] = "my_session" # Make sure this session actually exists. You can create a new session in the UI.
+```
+
+2. To switch sessions mid-script or mid-notebook, do NOT set the `LANGCHAIN_SESSION` environment variable. Instead: `langchain.set_tracing_callback_manager(session_name="my_session")`