Inspect Runnables

• Author: ranian963

• Peer Review:

• This is a part of LangChain Open Tutorial

Overview

In this tutorial, we introduce how to inspect and visualize various components (including the graph structure) of a Runnable chain. Understanding the underlying graph structure can help diagnose and optimize complex chain flows.

Table of Contents

• Overview

• Environment Setup

• Introduction to Inspecting Runnables

  • Graph Inspection

  • Graph Output

  • Prompt Retrieval

  References

• LangChain: Runnables

• LangChain Open Tutorial

---

Environment Setup

Set up the environment. You may refer to Environment Setup for more details.

[Note]

• langchain-opentutorial is a package that provides a set of easy-to-use environment setup, useful functions and utilities for tutorials.

• You can checkout the langchain-opentutorial for more details.

%%capture --no-stderr
%pip install langchain-opentutorial

from langchain_opentutorial import package

package.install(
    [
        "langsmith",
        "langchain",
        "langchain_core",
        "langchain_community",
        "langchain_openai",
        "faiss-cpu",
        "grandalf",
    ],
    verbose=False,
    upgrade=False,
)

# Set environment variables
from langchain_opentutorial import set_env

set_env(
    {
        "OPENAI_API_KEY": "",
        "LANGCHAIN_API_KEY": "",
        "LANGCHAIN_TRACING_V2": "true",
        "LANGCHAIN_ENDPOINT": "https://api.smith.langchain.com",
        "LANGCHAIN_PROJECT": "02-InspectRunnables",
    }
)

You can alternatively set OPENAI_API_KEY in .env file and load it.

[Note] This is not necessary if you've already set OPENAI_API_KEY in previous steps.

from dotenv import load_dotenv

load_dotenv(override=True)

Introduction to Inspecting Runnables

LangChain Runnable objects can be composed into pipelines, commonly referred to as chains or flows. After setting up a runnable, you might want to inspect its structure to see what's happening under the hood.

By inspecting these, you can:

• Understand the sequence of transformations and data flows.

• Visualize the graph for debugging.

• Retrieve or modify prompts or sub-chains as needed.

Graph Inspection

We'll create a runnable chain that includes a retriever from FAISS, a prompt template, and a ChatOpenAI model. Then we’ll inspect the chain’s graph to understand how data flows between these components.

from langchain_core.prompts import ChatPromptTemplate
from langchain_community.vectorstores import FAISS
from langchain_core.output_parsers import StrOutputParser
from langchain_core.runnables import RunnablePassthrough
from langchain_openai import ChatOpenAI, OpenAIEmbeddings

# Create a FAISS vector store from simple text data
vectorstore = FAISS.from_texts(
    ["Teddy is an AI engineer who loves programming!"], embedding=OpenAIEmbeddings()
)

# Create a retriever based on the vector store
retriever = vectorstore.as_retriever()

template = """Answer the question based only on the following context:\n{context}\n\nQuestion: {question}"""
# Create a prompt template
prompt = ChatPromptTemplate.from_template(template)

# Initialize ChatOpenAI model
model = ChatOpenAI(model="gpt-4o-mini")

# Construct the chain: (dictionary format) => prompt => model => output parser
chain = (
    {
        "context": retriever,
        "question": RunnablePassthrough(),
    }  # Search context and question
    | prompt
    | model
    | StrOutputParser()
)

Graph Output

We can inspect the chain’s internal graph of nodes (steps) and edges (data flows).

# Get nodes from the chain's graph
chain.get_graph().nodes

# Get edges from the chain's graph
chain.get_graph().edges

We can also print the graph in an ASCII-based diagram to visualize the chain flow.

chain.get_graph().print_ascii()

Prompt Retrieval

Finally, we can retrieve the actual prompts used in this chain. This is helpful to see exactly what LLM instructions are being sent.

chain.get_prompts()