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How-to guides

Here you'll find answers to “How do I….?” types of questions. These guides are goal-oriented and concrete; they're meant to help you complete a specific task. For conceptual explanations see Conceptual Guides. For end-to-end walkthroughs see Tutorials. For comprehensive descriptions of every class and function see API Reference.

Installation​

Key features​

This highlights functionality that is core to using LangChain.

LangChain Expression Language (LCEL)​

LangChain Expression Language is a way to create arbitrary custom chains. It is built on the Runnable protocol.

LCEL cheatsheet: For a quick overview of how to use the main LCEL primitives.

Components​

These are the core building blocks you can use when building applications.

Prompt templates​

Prompt Templates are responsible for formatting user input into a format that can be passed to a language model.

Example selectors​

Example Selectors are responsible for selecting the correct few shot examples to pass to the prompt.

Chat models​

Chat Models are newer forms of language models that take messages in and output a message.

LLMs​

What LangChain calls LLMs are older forms of language models that take a string in and output a string.

Output parsers​

Output Parsers are responsible for taking the output of an LLM and parsing into more structured format.

Document loaders​

Document Loaders are responsible for loading documents from a variety of sources.

Text splitters​

Text Splitters take a document and split into chunks that can be used for retrieval.

Embedding models​

Embedding Models take a piece of text and create a numerical representation of it.

Vector stores​

Vector stores are databases that can efficiently store and retrieve embeddings.

Retrievers​

Retrievers are responsible for taking a query and returning relevant documents.

Indexing​

Indexing is the process of keeping your vectorstore in-sync with the underlying data source.

Tools​

LangChain Tools contain a description of the tool (to pass to the language model) as well as the implementation of the function to call.

Agents​

note

For in depth how-to guides for agents, please check out LangGraph documentation.

Callbacks​

Callbacks allow you to hook into the various stages of your LLM application's execution.

Custom​

All of LangChain components can easily be extended to support your own versions.

Generative UI​

Multimodal​

Use cases​

These guides cover use-case specific details.

Q&A with RAG​

Retrieval Augmented Generation (RAG) is a way to connect LLMs to external sources of data. For a high-level tutorial on RAG, check out this guide.

Extraction​

Extraction is when you use LLMs to extract structured information from unstructured text. For a high level tutorial on extraction, check out this guide.

Chatbots​

Chatbots involve using an LLM to have a conversation. For a high-level tutorial on building chatbots, check out this guide.

Query analysis​

Query Analysis is the task of using an LLM to generate a query to send to a retriever. For a high-level tutorial on query analysis, check out this guide.

Q&A over SQL + CSV​

You can use LLMs to do question answering over tabular data. For a high-level tutorial, check out this guide.

Q&A over graph databases​

You can use an LLM to do question answering over graph databases. For a high-level tutorial, check out this guide.

LangGraph.js​

LangGraph.js is an extension of LangChain aimed at building robust and stateful multi-actor applications with LLMs by modeling steps as edges and nodes in a graph.

LangGraph.js documentation is currently hosted on a separate site. You can peruse LangGraph.js how-to guides here.

LangSmith​

LangSmith allows you to closely trace, monitor and evaluate your LLM application. It seamlessly integrates with LangChain and LangGraph.js, and you can use it to inspect and debug individual steps of your chains as you build.

LangSmith documentation is hosted on a separate site. You can peruse LangSmith how-to guides here.

Evaluation​

Evaluating performance is a vital part of building LLM-powered applications. LangSmith helps with every step of the process from creating a dataset to defining metrics to running evaluators.

To learn more, check out the LangSmith evaluation how-to guides.

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