Exploring the best syntax highlighting libraries

Have you ever tried to read through an incorrectly formatted or highlighted block of code? It’s like trying to navigate a dense forest without a map.

Thankfully, syntax highlighting has come a long way since its early days in the 1970s, when it was introduced in the Emacs text editor. Today, several syntax highlighting libraries are available to developers, each with its strengths and weaknesses.

But why is syntax highlighting so important? It makes code easier to read, write, and debug.

By visually distinguishing between different program elements, such as keywords, comments, and strings, syntax highlighting helps developers quickly understand the structure and logic of a piece of code. This not only improves productivity but also reduces the likelihood of syntax errors.

In the image below, you can compare an example of a code snippet with syntax highlighting on the left and another without on the right:

In this article, we’ll look at some of the best syntax highlighting libraries available today and explore their unique features and benefits. The libraries we’ll cover include the following:

• Highlight.js
• Microlight.js
• Bright
• starry-night
• react-syntax-highlighter
• Torchlight
• Chroma

Jump to the end to view a comparison table for all the libraries.

Highlight.js

Highlight.js is an open source JavaScript library that brands itself generally as “syntax highlighting for the web.” It lives up to its name, as it’s the most widely used and actively maintained syntax highlighting library by web developers.

The library is designed to support over 190 programming languages, with the option of adding third-party language definitions to support even more languages. It can be customized with over 240 color themes to suit your style preferences.

Highlight.js works by scanning the webpage for code blocks marked up inside a <pre><code> tag or with the language defined explicitly in the class attribute and applying syntax highlighting to them. The library also provides more flexibility by allowing developers to determine what code blocks should have syntax highlighting manually applied and what color theme should be used.

Some of the key features of Highlight.js include the following:

• Easy installation and setup
• Automatic language detection
• Multi-language code highlighting
• Support for usage in Node.js

While Highlight.js is a commonly favored library for numerous projects because of its many benefits, it is essential to recognize that it also possesses certain limitations, including:

• Relatively large size can increase your application’s page load time
• Limited support for modern JavaScript frameworks

Microlight.js

Microlight.js is a lightweight, compact, open source syntax highlighting library. It’s about 2.2KB in size and provides a very straightforward process for adding syntax highlighting to code on a webpage.

This library takes a different approach to syntax highlighting by using a colorless highlighting mechanism that alters the look and feel of the font instead of using a color theme to highlight syntax elements in a code block. This helps ensure it matches the overall design and provides the added benefit of not shipping additional CSS.

Unlike other libraries that use a set of rules for different programming languages to apply syntax highlighting, Microlight.js uses a language-agnostic highlighting strategy that goes through the code and highlights it. This approach frees the developer from specifying the language of the code and makes it possible to highlight code containing different programming languages.

Although Microlight.js offers several benefits that make it a library of choice for your projects, certain drawbacks are worth mentioning:

• The project is not actively maintained
• No built-in support for modern JavaScript frameworks
• Limited customization options for color themes and languages

Bright

Bright is an open source library built on React Server Components. It’s easy to set up and install, with minimal configuration needed to add code snippets with syntax highlighting in a React application. Additionally, it provides different color theme options and the ability to add custom-made themes with the library’s theme editor.

Bright’s use of React Server Components provides various benefits. Most significantly, the pre-processing workload required for syntax highlighting is moved to the server, which is more performant and efficient for handling large code snippets. Therefore, rendering will be the only operation done on the client side.

Also, by using React Server Components, the amount of client-side JavaScript code sent to the browser is significantly reduced to help improve the page load time.

The library has an extension system that provides developers with a flexible way to customize the syntax highlighting experience and include a range of additional features. Some of the capabilities of the extension system include:

• Code folding
• Line highlighting
• File icons
• Interactive elements (e.g., links, buttons)

More of these features can be found on the project’s recipe page.

While Bright is a library of choice for many projects due to its various benefits, it is essential to note that there are certain drawbacks associated with it, some of which include the following:

• Cannot be used outside the React ecosystem
• Only supports versions of React that are compatible with Server Components
• Extension system is complex and requires significant effort to implement customizations

starry-night

starry-night is a JavaScript syntax highlighting library built as an open source version of the PrettyLights project, which is a closed source syntax highlighting library used internally by GitHub since 2014.

The library supports over 520 grammars, or sets of rules that define the syntax and structure of a particular programming language. However, this support for a wide range of programming languages results in the package being heavy in size, which is a cause for concern, especially for usage in browsers.

By default, starry-night uses the same theme GitHub uses for syntax highlighting on its website. It also supports other color themes for dark and light modes, including the flexibility to add your custom themes.

starry-night was designed to output an abstract syntax tree (AST) before it’s converted into a format that’s compatible with the target destination. This is helpful for syntax highlighting where serialized HTML won’t work well — i.e., CLIs and virtual DOM frameworks like React, Preact, Vue, or others.

This approach is beneficial for performance because the generated AST is easier to highlight without performing costly regular expression matching, especially for large code snippets.

Some other features of starry-night include the following:

• Compatible with major JavaScript execution environments, such as web browsers, Node.js, and Deno
• Easily extended to support more programming languages and color themes
• Support for plugins to extend the default features (e.g., adding line numbers)

Although starry-night is a preferred library for many projects due to its numerous advantages, it is crucial to acknowledge that it also has some limitations, including:

• The grammar system may require some expertise to create or customize grammars for new or existing programming languages
• The library was built to support only ES modules, which may not be compatible with older versions of browsers and Node.js
• The library’s size may not be suitable for use in browsers

react-syntax-highlighter

react-syntax-highlighter is an open source library that uses components to add syntax highlighting to code blocks in a React application. It’s simple to install and has an easy-to-use API with options for configuring the syntax highlighting experience, such as adding line numbers and overriding the default styles.

The library also allows developers to use Highlight.js — the default option — or Prism for syntax highlighting, which comes with the benefits of rich language support and a variety of color themes.

react-syntax-highlighter uses the lowlight and refractor packages under the hood to generate a syntax tree of the highlighted code snippet to build the virtual DOM before the real DOM gets updated. The approach is beneficial when a change occurs because React can efficiently update affected parts of the DOM instead of completely overwriting it.

Some other features of react-syntax-highlighter include the following:

• Supports server-side rendering
• Supports adding custom language definitions and color themes
• Supports adding a custom renderer to modify how code snippets are rendered
  • Can be helpful when highlighting large blocks of code

While react-syntax-highlighter is a widely used library that offers many benefits, it’s essential to recognize its limitations. These limitations include:

• It can’t be used outside the React ecosystem
• The size of the library is relatively large and can impact the overall size of your application bundle

Torchlight

Torchlight is an HTTP API for quickly adding syntax highlighting to code blocks in a web application. It’s majorly targeted at applications built within the Laravel/PHP ecosystem.

Powered by VS Code’s parsing engine and language grammars, Torchlight provides developers with top-notch support for various programming languages and several color themes that VS Code supports.

Torchlight also makes it very easy to control how your code is rendered to add features that improve the syntax highlighting experience using comments in your code blocks. Some features you can add include focusing lines, diffs, collapsing lines, and more.

Unlike other syntax highlighting libraries we’ve discussed, Torchlight does not need to run on the client’s browser to add syntax highlighting. It’s used as an installable server-side client that operates as a middleware in a web application by scanning the page for specific code blocks sent to their API, which processes it and returns highlighted code to be inserted in the response.

This syntax highlighting technique provides the following benefits:

• No JavaScript is sent to the browser
• Highlighted code snippets can be easily cached to improve performance
• The pre-processing workload required for syntax highlighting is done on the server to improve the user experience

Although Torchlight has many benefits that make it the tool of choice for syntax highlighting in your web applications, the following drawbacks are worth mentioning:

• Their API can be costly for users who make a large number of requests
• Syntax highlighting won’t be available on your web application when there’s a downtime
• Only compatible with web applications that are built for their first-party integrations

Chroma

Chroma is a versatile open source syntax highlighting library written in Go and heavily inspired by Pygments. It’s the library of choice for Go developers who want to add syntax highlighting to various programming languages in their applications.

Chroma is built on the concept of lexers, formatters, and styles:

• Lexers break down input text into a series of tokens that can be classified and highlighted
• Styles determine how each token is highlighted, including color and other visual attributes
• Formatters then take the stream of tokens and styles and output them in a specific format, such as HTML or terminal output

The Chroma library was designed to be modular to provide developers the flexibility of implementing their lexers, formatters, and styles to add support for more languages.

Other relevant features of Chroma include the following:

• Designed as an installable software package or CLI, depending on your use case
• Support for a wide range of programming languages and color themes
• Support for multiple output formats, including HTML, SVG, Terminal Output, ANSI escape sequences
• Easy to use and straightforward API for adding syntax highlighting

Chroma is a powerful and versatile syntax highlighting library, but it does have a few drawbacks that developers should be aware of:

• Chroma is written in Go, which can be a hindrance for developers who aren’t familiar with it
• Documentation can be challenging for developers who are new to the Go ecosystem
• Limited support for some esoteric languages

Comparing syntax highlighting libraries

Many options are available when choosing a syntax highlighting library for your project. Each library has strengths and weaknesses, and deciding which one to use is challenging.

It’s important that you carefully consider factors like language support, customizability, performance, compatibility, community support, licensing, and accessibility to make a well-informed decision.

Here’s a table comparing the libraries based on popularity, languages supported, color themes, and customization:

Conclusion

Whether you’re looking for a simple, lightweight library for a small project or a more feature-rich option for a larger application, there’s sure to be a syntax highlighting library that fits your needs.

We hope this article has provided you with a useful overview of some of the best options. Don’t hesitate to experiment and try different options until you find the best option.