Astro vs. Next.js: Features, performance, and use cases compared

Astro is a new JavaScript framework that can be used as an alternative to Next.js. Each takes a different approach and provides different developer advantages when building web applications, so which is best for your next project?

This guide for developers explains the practical differences between Astro and Next.js, covering their purpose, features, architectures, and learning curve, to help you choose the right one for your use case.

What is Next.js?

Next.js is one of the most widely used React frameworks designed for building statically hosted websites and JavaScript applications that use server-side rendering. Next.js is open source and is backed by Vercel, which uses it as part of their online app development and hosting platform.

The purpose of Next.js is to provide tools for building websites, including those that use client-side rendering (CSR), static site generation (SSG) and server-side rendering (SSR). SSG pre-generates all files for an app so that they can be hosted statically (without requiring server-side processing using tools like Node.js or PHP) as simple files, often on low-cost, high-performance object storage or content delivery networks (CDNs). SSR, on the other hand, dynamically generates web pages on the server (in the case of Next.js using Node.js), which allows for unique content to be included on each page without it being fetched from an API.

The key features of Next.js for developers include:

• Support for both SSR and SSG (or a combination of the two): Next.js provides flexibility in when and how data is loaded. SSR is able to include unique data in the initial page load at the cost of requiring server-side processing, whereas SSG can deliver static content faster and load additional data via subsequent API calls at the cost of more calls and relying on the performance of the API.

• Included routing with automatic page/file-based routing: Rather than writing routes manually, Next.js can automatically generate routes by mapping application routes to the file structure. Dynamic routing is also supported, allowing more flexibility in how your URLs are presented.

• Automatic code splitting: Code can be automatically split according to its route, improving page load speeds and reducing errors by isolating each page before it is sent to the user.

• Automatic image optimization: The Next.js image component automatically resizes and optimizes images to improve performance, and it provides lazy-loading to further reduce initial page load times.

• Built-in internationalization: Implementing support for different regions and languages is supported by internationalization routing.

• Included CSS and Sass support: External style sheets can be used, or CSS can be scoped to the current component, making it easier to avoid CSS naming conflicts. CSS-in-JS is also supported for dynamically applying styles.

Next.js is ideal for building full-stack web applications with interactive, app-like experiences that heavily rely on dynamic data. Well-known products that were built using Next.js include Hulu, Twitch, Reddit, and Product Hunt. These examples highlight the importance of SSR in making large amounts of constantly updated content immediately available.

If you're new to Next.js, check out our Contentful Next.js starter project to get up and running, or start building using one of our Next.js marketing, ecommerce, or blog templates.

What is Astro?

Astro is a more recent arrival on the JavaScript framework scene, offering developers a framework that focuses on SSG (with some support for SSR) and that is heavily optimized for speed. Astro is also open source, with an active developer community and users including the likes of Google and Microsoft.

The purpose of Astro is building websites with a focus on static content that doesn't frequently change. For example, once a blog page has been written and published, its contents are unlikely to be modified, making it appropriate for serving from static hosting. This means it'll load faster, as everything is pre-rendered and doesn't have to be queried from a database, assembled into a page, and then sent to the user. It's also ideal for applications that retrieve all of their data from APIs that can have their code statically hosted.

The headline features of the Astro JavaScript framework include:

• Performance as a priority: Astro is designed around delivering content-rich websites as quickly as possible, leveraging static hosting, CDNs, minification, and automatic optimization to load content as quickly as possible.

• A focus on SSG and page load speed: By focusing on static site generation, Astro can optimize heavily for static hosting. However, it also includes tools for SSR when it's needed for dynamic content.

• Unique “Islands” architecture: The Astro Islands architecture reduces load times by only sending the necessary JavaScript to the browser based on specified elements or the viewport.

• Markdown/MDX support: Astro support lets you create your blog posts, product descriptions, and other web pages in Markdown. This lets you store your content as files rather than waiting for a database, and it also makes it possible to use Git-based workflows to manage content.

• Automatic optimization: Images are automatically optimized (remote image optimization tools can also be integrated to optimize remote images) and JavaScript/CSS minification is included. Like React, styles can be scoped, and CSS-in-JS can be implemented with supported libraries.

Astro is best suited for websites that aren't reliant on up-to-the-minute data (like content aggregation sites or social media), and more suited to sites that can be pre-generated periodically when new content is published; for example, news sites, galleries, portfolios, or product websites that receive daily updates. This allows the sites to be pre-generated when they change and deployed to fast static hosting with a CDN for the best possible performance and SEO impact.

Popular websites built with Astro include the Google Firebase Blog, Trivago Tech Blog, and The Guardian's Engineering blog, demonstrating the focus on content in Astro's real-world use cases.

You can get started with Astro using the Contentful Astro Starter and learn more about how you can get the most out of Astro and Contentful in the Astro documentation

Architecture and deployment options: SSG vs SSR

When choosing between Astro vs. Next.js, deployment and architecture must be considered. While there are more steps involved in SSG, it is no more complex to deploy than SSR, and it offers improved performance when paired with a CDN.

Comparing Astro with other JavaScript frameworks usually leads to a discussion about server-side generation and server-side rendering. Here are more details, and the advantages, of each approach:

• Static site generation (SSG) uses a build process to pre-render pages to static HTML files that can then be deployed to static hosting. This is SEO-friendly, as individual pages can be indexed in their complete form, and it can lead to higher performance when hosted using a CDN.

• Server-side rendering (SSR) renders pages dynamically on the server for each request. This is ideal for regularly updated content or content that will be different for each page load, but it can lead to longer wait times, since pages must be assembled before they are sent to the browser.

• Client-side rendering (CSR) renders pages in the browser using JavaScript, which is common for single-page app (SPA) frameworks. This is done after all of the data for rendering everything in the web application has been downloaded, and while it's ideal for highly interactive and app-like applications, it’s detrimental to page load times and SEO.

• Incremental static regeneration (ISR) is a combination of SSG with CSR that periodically updates only the portions of a web page that need to change. This combines SEO-friendly initial page loads of static content with the ability to update the page with new content.

SSG and CSR do not require a back end to function after the initial build process has deployed the static files. SSR and ISR require a runtime environment running on a backend server to render content before it’s delivered to users' web browsers.

Next.js supports SSG, SSR, and CSR, whereas Astro supports SSG with limited SSR. This will affect your choice, as in some use cases a focus on SSG will limit what you can do, whereas in other use cases it will be ideal for meeting usability, performance, and SEO requirements.

The Astro Islands architecture is not tied to any of the above concepts and works regardless of the deployment method. Islands is a form of selective hydration, keeping the page itself static while only loading the JavaScript for specific interactive elements (with the option of doing so only as they appear in the browser's view window). Islands functionality doesn't require any special coding to use: it works with existing user interface (UI) libraries (even allowing for multiple UI libraries to be used simultaneously as islands are independent), component libraries, and your own UI code.

Is Astro better than Next.js?

Just because something is newer doesn't mean it is better; however, it does mean that it can address some issues that established solutions cannot directly address without significant reworking. In this case, however, Next.js and Astro both focus on different use cases: neither is better, but one just may be more suitable for your specific project.

Next.js was specifically developed for building complex, dynamic applications that behave like native apps, while Astro was built for static websites focusing on marketing and content, and optimized for performance and SEO. Before you choose Astro or Next.js for your project, you should carefully assess which features you require to meet your project's goals and choose the framework that is the best fit.

Feature comparison: Choosing between Next.js and Astro

The overall goal of any framework is to speed up the development of applications, so choosing whether Next.js or Astro is best for your project will depend on what your project’s goals are and which tool provides the features that best enable them.

If your project requires state management, dynamic routing, API routes, and other features for building apps instead of static websites, Next.js is the clear choice. 

However, if you are building a static site or resource that uses structured data or you want to quickly kick off a project with limited functionality, you may want to consider Astro as an alternative due to its simplicity — using a complex tool like Next.js where it isn't required may not be the best use of resources.

Code samples: Comparing Next.js and Astro

Below are two simple “Hello world” examples in Next.js and Astro. Both use React to display a button that increments a counter, but there are differences in the syntax.

Next.js code example

Notice that:

• The index.js file is stored in the pages directory, meaning that a route is automatically created for it at /.

• The syntax is all React-based, and components are used directly, without additional directives.

Astro code example (with islands)

The below example demonstrates the Astro Islands feature by separating the static and interactive parts of the page so that they can be loaded separately:

Note the following in the above example:

• Additional Astro syntax (the code fence) is required when integrating JavaScript (including when creating React components).

• The Astro client:load directive is used to make the button immediately interactive. Without this, Astro would serve a static page with the JavaScript stripped out. You could also use the client:visible directive which would only load the required JavaScript for the interactive button when it enters the viewport, further improving initial page load performance.

• The contents of the <h1> and <p> tags are completely static and do not need any JavaScript, meaning they can be rendered by Astro before sending any JavaScript to the browser for a fast initial page load.

• The HelloButton React component is interactive and is included with the client:load directive. This creates a dynamic “island,” and only the JavaScript for this island is loaded, allowing the rest of the page to remain static.

• You could also add Vue or any other UI framework components in their own islands without them conflicting.

This also demonstrates how Astro is geared toward sites with minimal interactivity, allowing it to be isolated so that static content can be loaded faster.

Static sites need a high-performance, composable back end

Once you've chosen Astro vs. Next.js for your project, you'll need to consider your backend services architecture. While Next.js can provide its own backend functionality with features like API routes, it requires extra code to build and maintain. Many developers are eschewing this approach in favor of a composable architecture that combines several APIs to provide fast, prebuilt, and reliable functionality for their websites and applications.

The Contentful® Composable Content Platform combines a headless CMS with a fast, global CDN and content creation and curation tools (including live previews so you can see exactly what your published text, images, video, and other content look like. You can build apps in Astro or Next.js and deploy them on static hosting — which means lower hosting overheads and maintenance costs — and by leveraging our REST and GraphQL APIs, your statically hosted applications can include all of the interactive features and dynamic data your users expect without having to deploy your own servers.

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