What is LangChain? Build LLM Apps Easily with Python

LangChain is an open-source Python framework designed to make it easy to build applications powered by large language models (LLMs) like ChatGPT. It provides components to manage prompts, chain logic, memory, tools, and more.

Whether you’re building a chatbot, a document search tool, or an agent that uses tools like calculators or web search, LangChain simplifies the process.

Table of Contents

Why LangChain?

Imagine you want to build a customer support chatbot that can:

  • Understand user questions
  • Retrieve relevant documents
  • Summarize answers
  • Respond like a helpful assistant

Doing this manually with raw API calls is complex and messy.
LangChain connects all these pieces into reusable, well-structured components—like building blocks for LLM applications.

Core Features of LangChain

1. PromptTemplate

Create reusable and dynamic prompts.

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from langchain.prompts import PromptTemplate

template = "You are a helpful assistant. Question: {question}"
prompt = PromptTemplate.from_template(template)

print(prompt.format(question="What is Python?"))

Combine a prompt and a model to process user input.

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from langchain.llms import OpenAI
from langchain.chains import LLMChain

llm = OpenAI(model_name="gpt-3.5-turbo", temperature=0.7)
chain = LLMChain(llm=llm, prompt=prompt)

response = chain.run("What is LangChain?")
print(response)

Enable multi-turn conversations by storing chat history.

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from langchain.chains import ConversationChain
from langchain.memory import ConversationBufferMemory

conversation = ConversationChain(
    llm=llm,
    memory=ConversationBufferMemory()
)

print(conversation.run("Hello!"))
print(conversation.run("What did I just say?"))

Let LLMs use external tools like calculators or APIs with decision-making.

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from langchain.agents import load_tools, initialize_agent
from langchain.agents.agent_types import AgentType

tools = load_tools(["llm-math"]llm=llm)
agent = initialize_agent(
    tools, llm, agent=AgentType.ZERO_SHOT_REACT_DESCRIPTION, verbose=True
)

print(agent.run("What is 25 * 38?"))

Real-World Use Cases

  1. AI Chatbots – Context-aware assistants that remember conversations
  2. Document Q&A – Search and summarize internal knowledge bases
  3. AI Agents – Perform reasoning and take actions using tools
  4. Custom LLM APIs – Expose internal business logic via natural language

Benefits of LangChain

  • Modular: Build apps with pluggable components
  • Scalable: Suitable for small scripts or full-stack apps
  • Flexible: Works with OpenAI, HuggingFace, Cohere, and more
  • Memory-friendly: Maintain context across conversations
  • Tool Integration: Connect to databases, search engines, APIs, etc.

Limitations of LangChain

  • Learning curve: Some abstractions may be confusing at first
  • Debugging chains: Chained components can make tracing bugs harder
  • Performance overhead: Complex chains may increase latency

Summary

LangChain helps developers go beyond simple prompts by offering a structured way to build intelligent LLM-powered applications.

Whether you’re building a chatbot, a Q&A assistant, or an autonomous AI agent, LangChain gives you the tools to do it cleanly, scalably, and with less code.

Ready to build your own LLM app? Try LangChain today and start chaining your ideas into reality.