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Learn GraphQL

Ask an API for exactly the data you need, in one request.

Free to start. Built from a single prompt. No credit card.

GraphQL is a query language for APIs and a runtime for answering those queries, first built at Facebook and released publicly in 2015. A server publishes a typed schema describing its data, and clients send queries that name exactly which fields they want, usually to a single endpoint. That avoids fetching too much or making many round trips. Changes go through mutations, and live updates can use subscriptions. On the server, resolver functions fetch each field's data. Learnr builds a personalized GraphQL course from one prompt and teaches it with short lessons that end in a working API.

How to learn GraphQL, step by step

Query a public API in an explorer. Open a public GraphQL API in GraphiQL or a similar explorer and write queries using autocomplete. Try nested fields, arguments and variables before you build anything, so the client side makes sense first.
Learn the schema definition language. Write types for a book club app with Book, Author and Review, using non-null markers and lists. Add Query and Mutation root types and input types for creating records.
Build a server with resolvers. Use a server library such as Apollo Server or GraphQL Yoga in Node.js, or Strawberry in Python. Write resolvers that return data from an in-memory array first, then from a real database.
Add mutations, validation and auth. Implement create and update mutations, validate input, and pass the logged-in user through the context object. Decide which fields each user may read, since GraphQL exposes a flexible surface.
Fix the N+1 problem and limit query cost. Log database calls and watch a list of books trigger one author query each. Batch them with DataLoader, and add depth or complexity limits so a single query cannot overload the server.
Consume it from a front end. Connect a React app with Apollo Client, urql or plain fetch and render loading and error states. Regular Learnr lessons help keep schema syntax and resolver patterns fresh as you build.

What you'll learn

Write queries with fields, arguments, aliases and fragments
Design a schema with types, enums, inputs and non-null fields
Implement resolvers that read from a database
Add mutations and handle errors
Avoid the N+1 problem with batching through DataLoader

What's inside your GraphQL course

A sample path Learnr builds for GraphQL. Your real course adapts to your goal and level.

1. Why GraphQL exists and how it compares to REST
2. Queries, variables and fragments
3. Schema definition language and types
4. Resolvers, context and data sources
5. Mutations, errors and authorization
6. Performance, caching and client libraries

How long does it take to learn GraphQL?

Writing queries against an existing API takes a few days. Building your own GraphQL server with a database, auth and batching usually takes 3 to 6 weeks at 5 to 8 hours a week if you already know a backend language.

What you need before you start

JavaScript or another backend language, plus a basic understanding of HTTP, JSON and how APIs work. Knowing REST first makes GraphQL's trade-offs easier to see.

Common mistakes to avoid

Treating GraphQL as a database query language. It sits in front of your data sources, and resolvers still decide how data is fetched.
Ignoring the N+1 problem until production is slow. Batch related lookups with DataLoader or a similar tool from the start.
Assuming a typed schema means data is secure. Check authorization in resolvers for every sensitive field.

How Learnr builds your course

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GraphQL questions, answered

Is GraphQL replacing REST?

No. Both are widely used. GraphQL suits apps with many clients or complex nested data, while REST is simpler and caches easily over HTTP. Many companies run both.

Do I need a special database for GraphQL?

No. GraphQL works with any data source, including PostgreSQL, MongoDB, other REST APIs or files, because resolvers decide where each field comes from.