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LangChain 101

A practical guide series for learning LangChain - prompts, models, retrieval, tools, and exactly where LangChain's job ends and LangGraph's begins. Written by people who build with it for a living.

Foundations → Practitioner · ~53 minutes total
| | input Prompt template Model any provider Parser output

LangChain's core pattern: pipe simple pieces together with | to build a chain.

FOUNDATIONS

Start Here

New to LangChain, or coming from the LangGraph guides and wondering how the two fit together? Start here.

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What Is LangChain? (And How It Relates To LangGraph)

The toolbox versus the wiring diagram - what LangChain actually gives you, and exactly where it hands off to LangGraph.

Foundations 5 min read
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Prompts, Models & Output Parsers

The three pieces you'll chain together in almost every LangChain project, and how LCEL's pipe syntax connects them.

Foundations 6 min read
HANDS-ON

Work With Real Data

Where LangChain earns its keep - connecting a model to documents it wasn't trained on.

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Retrieval & RAG

Load, split, embed, store, retrieve - the five-stage pipeline behind every "chat with your documents" app.

Hands-On 7 min read

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ADVANCED

Tools, Agents & Memory

The two areas where LangChain's own guidance has shifted the most recently - worth getting the current picture, not an outdated one.

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Tools & Tool-Calling Agents

Giving a model access to a tool, and the current, non-deprecated way to build an agent around that.

Advanced 6 min read
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Memory in LangChain

Why the old memory classes are deprecated, and what to reach for instead in a project you're starting today.

Advanced 5 min read
GO DEEPER

Go Deeper

The mechanics underneath everything above, plus how to actually know if a change made your chain better.

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LCEL: Composing Chains with the Pipe Operator

What the | operator actually does, and why LCEL chains get streaming and async for free.

Go Deeper 6 min read
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Document Loaders and Text Splitters

The step before retrieval: getting documents in, and splitting them into chunks that actually retrieve well.

Go Deeper 6 min read
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Structured Output and Function Calling

Getting a model to reliably return JSON matching a schema, and when that beats reaching for a full agent.

Go Deeper 6 min read
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Evaluating LangChain Apps with LangSmith

How to tell whether a prompt or chunking change actually made your chain better, instead of guessing.

Go Deeper 6 min read