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Extract OpenInference inferences and traces to visualize and troubleshoot your LLM Application in Phoenix
Phoenix has first-class support for LangChain applications. This means that you can easily extract inferences and traces from your LangChain application and visualize them in Phoenix.


Traces provide telemetry data about the execution of your LLM application. They are a great way to understand the internals of your LangChain application and to troubleshoot problems related to things like retrieval and tool execution.
To extract traces from your LangChain application, you will have to add Phoenix's OpenInference Tracer to your LangChain application. A tracer is a class that automatically accumulates traces (sometimes referred to as spans) as your application executes. The OpenInference Tracer is a tracer that is specifically designed to work with Phoenix and by default exports the traces to a locally running phoenix server.
To view traces in Phoenix, you will first have to start a Phoenix server. You can do this by running the following:
import phoenix as px
session = px.launch_app()
Once you have started a Phoenix server, you can start your LangChain application with the OpenInference Tracer as a callback. There are two ways of adding the `tracer` to your LangChain application - by instrumenting all your chains in one go (recommended) or by adding the tracer to as a callback to just the parts that you care about (not recommended).
Instrument Langchain
Use callbacks
We recommend that you instrument your entire LangChain application to maximize visibility. To do this, we will use the LangChainInstrumentor to add the OpenInferenceTracer to every chain in your application.
from phoenix.trace.langchain import OpenInferenceTracer, LangChainInstrumentor
# If no exporter is specified, the tracer will export to the locally running Phoenix server
tracer = OpenInferenceTracer()
# If no tracer is specified, a tracer is constructed for you
# Initialize your LangChain application
# Note that we do not have to pass in the tracer as a callback here
# since the above instrumented LangChain in it's entirety.
response =
If you only want traces from parts of your application, you can pass in the tracer to the parts that you care about.
from phoenix.trace.langchain import OpenInferenceTracer
# If no exporter is specified, the tracer will export to the locally running Phoenix server
tracer = OpenInferenceTracer()
# Initialize your LangChain application
# Instrument the execution of the runs with the tracer. By default the tracer uses an HTTPExporter
response =, callbacks=[tracer])
By adding the tracer to the callbacks of LangChain, we've created a one-way data connection between your LLM application and Phoenix. This is because by default the OpenInferenceTracer uses an HTTPExporter to send traces to your locally running Phoenix server! In this scenario the Phoenix server is serving as a Collector of the spans that are exported from your LangChain application.
To view the traces in Phoenix, simply open the UI in your browser.

Saving Traces

If you would like to save your traces to a file for later use, you can directly extract the traces from the tracer
To directly extract the traces from the tracer, dump the traces from the tracer into a file (we recommend jsonl for readability).
from phoenix.trace.span_json_encoder import spans_to_jsonl
with open("trace.jsonl", "w") as f:
Now you can save this file for later inspection. To launch the app with the file generated above, simply pass the contents in the file above via a TraceDataset
from phoenix.trace.utils import json_lines_to_df
json_lines = []
with open("trace.jsonl", "r") as f:
json_lines = cast(List[str], f.readlines())
trace_ds = TraceDataset(json_lines_to_df(json_lines))
In this way, you can use files as a means to store and communicate interesting traces that you may want to use to share with a team or to use later down the line to fine-tune an LLM or model.

Working Example with Traces

For a fully working example of tracing with LangChain, checkout our colab notebook.
Google Colaboratory
Troubleshooting an LLM application using the OpenInferenceTracer


Phoenix supports visualizing LLM application inference data from a LangChain application. In particular you can use Phoenix's embeddings projection and clustering to troubleshoot retrieval-augmented generation. For a tutorial on how to extract embeddings and inferences from LangChain, check out the following notebook.
Google Colaboratory
Evaluating and Improving Search and Retrieval Applications (LangChain, Pinecone)