Guide · Open source
How to use Koa: install it and build middleware-based servers
Updated · written with AI from the project's own documentation and checked against our catalogue data
Koa is an open-source web framework for Node.js. You use it to build HTTP servers and APIs by chaining middleware functions, and it uses ES2017 async/await so each step can wait for work such as a database call before passing control onward. This guide covers what you need before starting, how to install Koa, how its middleware model works, and whether it fits your project.
Koakoajs/koa · ★ 35.7k · MIT Install options & downloads Quick start
- 1Install Node.js. Make sure Node.js is installed on your machine, since Koa runs on Node.js.
- 2Create or open a project folder. Open the folder where your Node.js project lives, so Koa is installed into that project.
- 3Install Koa. Run npm install koa from inside the project folder to add Koa from npm.
- 4Add the packages you need. Koa does not include routing or body parsing, so add separate packages for those features as your project requires.
What you need before you install Koa
Koa runs on Node.js, so Node.js must be installed on your machine before anything else. Koa is a JavaScript project and is aimed at developers who already know how HTTP requests and responses work.
Koa ships with little built in, so this guide assumes you are comfortable with Node.js basics and with the idea of middleware. If you are brand new to Node.js, learn the basics first.
- Node.js installed
- Basic familiarity with JavaScript and HTTP
- Understanding of middleware, or experience with Express-style middleware
Install Koa with npm
Koa is installed from npm, the Node.js package manager. Run the install command from inside your project folder so Koa is added to that project.
The Koa project lists this as the install method in its README. Project details and documentation are available at koajs.com.
npm install koaHow Koa middleware works
In Koa, a web server is built by chaining middleware functions. Each middleware receives the request context and can do work before handing control to the next function in the chain.
Because Koa uses async/await, a middleware function can pause while it waits for slow work, such as a database query, and then continue. This keeps the flow of each step readable compared with nested callbacks.
- Each middleware runs in order through the chain.
- A middleware can await a database call or other async work.
- Control passes onward once the middleware finishes its step.
Add routing, body parsing and other features
Koa's core is intentionally small. Features such as routing and body parsing are not built in and come from separate packages that you choose and add yourself.
This is what lets you shape the framework to your project, but it also means you need to pick and maintain those add-ons. Teams that want everything included from the start may find this more setup than they want.
- Routing is provided by separate packages, not the Koa core.
- Body parsing is provided by separate packages, not the Koa core.
- You choose which add-ons to use, so the stack stays under your control.
Choose Koa or a similar Node.js framework
Koa is a good fit for Node.js developers who want a minimal framework they can shape, especially if they like Express-style middleware and want a smaller core. Teams building APIs or web servers who prefer async/await middleware will find it a natural match.
Other frameworks people compare it with include Express, Fastify, Hono and Restify. Each has its own design, so compare them against the features your project needs before deciding.
- Pick Koa for a minimal core you extend yourself.
- Pick a batteries-included framework if you want routing and parsing built in.
What people use it for
- Building a JSON API where each request passes through a chain of async middleware.
- Creating a custom web server where you control every add-on in the stack.
- Writing a Node.js backend for a team that prefers async/await over nested callbacks.
Frequently asked questions
Is Koa free to use?
Koa is released under the MIT licence, which is a permissive open-source licence. Check the MIT licence text and the project's repository for the exact terms before using it in a commercial product.
What do I need to install Koa?
Koa requires Node.js. Install Node.js first, then run npm install koa from your project folder.
Does Koa include routing?
No. Koa's core is small, and routing and body parsing come from separate packages that you add yourself.
What is the difference between Koa and Express?
Both use middleware-style design, and Koa is aimed at developers who want a smaller core and async/await middleware. Express is often compared with Koa, and Fastify, Hono and Restify are other options to consider.
Why is my Koa install not working?
This source does not list specific troubleshooting steps. Confirm Node.js is installed, run npm install koa from inside your project folder, and check the documentation at koajs.com for further help.
Is Koa a good first Node.js framework for beginners?
Koa is not ideal for complete beginners because it ships with little built in and assumes familiarity with HTTP and middleware. Learn basic Node.js first if you are new to it.
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Our verdict
Koa suits Node.js developers and teams who want a minimal, async/await-based framework that they can extend with their own add-ons. If you are a complete beginner or want routing and body parsing included out of the box, pick a more batteries-included framework instead.
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