What is the difference between build-time and runtime syntax highlighting?

Runtime highlighters like Prism and highlight.js load a JavaScript library in the visitor's browser, find the code blocks on the page, tokenize them, and wrap each token in colored markup after the page loads. Build-time highlighters like Shiki do that same tokenizing once, on your server or during your build, and bake the colored HTML straight into the page — so the browser downloads finished markup and runs no highlighting code at all. The practical consequence is bundle size and timing: runtime highlighting adds JavaScript the user must download and execute, and the code can flash unstyled for a moment before it runs, while build-time highlighting adds nothing to the client bundle but requires a build step and cannot highlight code that only exists after the page loads. For a blog or docs site where the code is known ahead of time, build-time is almost always the better trade; for a live playground or a comment box where users paste code, you need a runtime highlighter.

Why is Shiki's output so accurate?

Shiki does not write its own highlighting rules. It reuses the exact TextMate grammars and color themes that power Visual Studio Code, so a code block rendered by Shiki looks identical to the same code open in your editor, down to how it handles tricky constructs like template literals, JSX, and embedded languages. Prism and highlight.js use their own, lighter tokenizers — usually regex-based — which are fast and small but can mis-highlight complex or newer syntax that the VS Code grammars already handle. That fidelity is Shiki's main selling point and the reason it has become the default in modern documentation tooling. The cost of borrowing VS Code's grammars is weight: the grammar and theme data is large, which is one reason Shiki is designed to run at build time rather than ship to the browser.

Which syntax highlighter has the smallest bundle size?

Prism is generally the smallest when highlighting ships to the browser — its core is only a few kilobytes and you add just the languages and plugins you need, so a minimal setup can stay in the single-digit kilobyte range. highlight.js sits in the middle: it is heavier than a trimmed Prism because it bundles broad language support, though you can build a custom, smaller distribution with only the languages you use. Shiki is the heaviest if you run it in the browser, because it carries VS Code's grammar and theme data plus a regex engine, but that comparison is misleading for its normal use: Shiki is meant to run at build time, where it adds zero kilobytes to the client bundle. Treat specific byte figures as rough — they swing with how many languages, themes, and plugins you include — but the ordering holds: Prism lightest at runtime, Shiki effectively weightless at build time.

Can Shiki do dark mode and light mode together?

Yes, and it is one of the reasons people switch to it. Shiki can render a code block with two themes at once — a light theme and a dark theme — and emit CSS variables so the block follows the page's color scheme without re-highlighting or shipping a second copy of the markup. That means a single build-time pass gives you code that looks right in both modes, matching the rest of a site that toggles between light and dark. Prism and highlight.js handle themes with swappable CSS stylesheets, so dark mode is possible but you manage it yourself by loading the right stylesheet and toggling a class, rather than getting a dual-theme output for free.

Which code highlighter should I ship in a template I sell?

Match it to what the template is for. For a documentation site, blog starter, or any template where the code is written ahead of time, Shiki at build time gives editor-accurate output, dual light/dark themes, and zero client JavaScript — the look and performance buyers judge a modern template by. For a template with a live code editor, a playground, or anywhere users paste their own code after load, you need a runtime highlighter, and Prism is the lightest, most modular choice while highlight.js wins if you want automatic language detection with no configuration. Whichever you pick, wire it in behind one component or MDX setup so a buyer can swap it later, ship a sensible default theme, and make sure dark mode works out of the box, because a flash of unstyled or mis-colored code is one of the first things that makes a template feel unfinished.

Shiki vs Prism vs highlight.js (2026)

One Job, Three Very Different Approaches

Almost every developer project eventually has to show code on a web page — a documentation site, a blog, a component gallery, a landing page with a usage snippet. The moment you do, you need a syntax highlighter: the thing that turns a plain block of source into the colored, readable markup people expect. Three libraries dominate that choice in 2026: highlight.js, Prism, and Shiki.

They all do the same visible job, so it is tempting to treat them as interchangeable. They are not. The one decision that separates them — and the one to understand before anything else — is where the highlighting happens. highlight.js and Prism run in the visitor's browser, at runtime. Shiki runs on your server or during your build, ahead of time. That single difference drives everything else: bundle size, accuracy, theming, and how the code looks the instant the page appears.

We have compared the tools you write MDX with and the documentation frameworks you publish in. This guide is about the layer underneath both: how the code itself gets its colors.

highlight.js: The Batteries-Included Runtime Highlighter

highlight.js is the one you reach for when you just want code to look right with almost no setup. You include the library and a theme stylesheet, and it finds the code blocks on the page and highlights them.

What keeps it popular:

Automatic language detection. Point it at a code block with no language label and it guesses, often correctly. No other library in this list leans on auto-detection as a headline feature.
Huge language coverage out of the box. It ships support for 190+ languages, so obscure languages tend to just work without hunting for a plugin.
Drop-in simplicity. Two script and style tags, or one import, and you are highlighting. It runs anywhere JavaScript runs — browser or server.

highlight.js's superpower is that it is the fastest path from "I have code" to "it is highlighted," with language detection you do not have to think about. Its cost: it is a runtime library, so its JavaScript ships to and runs in the browser, it is heavier than a trimmed-down Prism, and auto-detection can guess wrong on short or ambiguous snippets. Its tokenizer is also lighter than VS Code's grammars, so very complex or brand-new syntax can be highlighted less precisely.

Prism: The Tiny, Modular Runtime Tokenizer

Prism takes the opposite stance to highlight.js on size. Its core is deliberately minimal, and you opt in to exactly the languages and features you need, so a lean setup stays remarkably small.

What sets it apart:

Smallest footprint at runtime. The core is only a few kilobytes; you add languages and plugins à la carte, which keeps a focused setup in the single-digit kilobyte range — the lightest option when highlighting ships to the browser.
A deep plugin ecosystem. Line numbers, line highlighting, copy-to-clipboard, command-line prompts, autolinking — Prism's plugins cover the things people bolt onto code blocks, and many frameworks and themes assume Prism is present.
Explicit and predictable. You declare the language on each block rather than relying on detection, which trades convenience for control and fewer surprises.

Prism's superpower is being the lightest, most modular runtime highlighter with a plugin for nearly every code-block feature you could want. Its cost: it still runs in the browser, you manage language and plugin includes yourself, and like highlight.js its regex-based tokenizer is less precise than VS Code's grammars on the hardest syntax. You also manage dark mode by swapping stylesheets rather than getting dual themes for free.

Colorful source code on a dark editor screen

Shiki: Build-Time, VS Code-Accurate, Zero Client JS

Shiki is the one developers keep switching to, and it has become the default highlighter in a lot of modern documentation tooling. Its defining idea: it reuses Visual Studio Code's own TextMate grammars and color themes, and it does the work at build time.

What makes it stand out:

Editor-accurate output. Because it borrows the exact grammars and themes that drive VS Code, a Shiki-rendered block looks identical to the same code in your editor, including tricky constructs other tokenizers mishandle.
Zero JavaScript in the browser. Shiki highlights once, during your build or on the server, and bakes finished colored HTML into the page. The client downloads static markup and runs no highlighting code — so there is no highlighter in your bundle and no flash of unstyled code.
Dual light and dark themes. It can render a block with a light and a dark theme at once and emit CSS variables, so code follows the page's color scheme with no second render and no extra markup.
Modern extras. Transformers for line and word highlighting, diff notation, focus, and the TypeScript-aware Twoslash integration that renders real type information inline.

Shiki powers the code blocks in tools like Astro and VitePress, which is a strong signal of where the ecosystem has landed for content sites.

Shiki's superpower is the most accurate output of the three, dual themes, and nothing added to the client bundle. Its cost: the grammar and theme data is large and setup is asynchronous, so running Shiki in the browser is heavy — it is built to run ahead of time. It also needs a build or server step, which means it cannot highlight code that only appears after the page loads, such as user-pasted input in a live editor.

Head-to-Head Comparison

Dimension	highlight.js	Prism	Shiki
Where it runs	Browser (runtime)	Browser (runtime)	Build time / server
Client JS added	Yes (medium)	Yes (smallest)	None
Accuracy	Good	Good	Editor-identical
Language detection	Automatic	Manual (per block)	Manual (per block)
Dual light/dark themes	Via stylesheet swap	Via stylesheet swap	Built in
Plugin ecosystem	Modest	Deep	Transformers + Twoslash
Best for	Drop-in, auto-detect	Lightest runtime	Static content, accuracy

Read it as three stances, not a scoreboard. The right highlighter is the one whose stance matches when and where your code gets highlighted.

How to Choose

Answer three questions.

Is the code known before the page loads? For a blog, docs site, or marketing page where the snippets are written ahead of time, Shiki at build time is the strongest default — accurate, dual-themed, and weightless on the client. If users paste or edit code after load (a playground, a live editor, a comment box), you need a runtime highlighter: Prism or highlight.js.
Do you want zero configuration, or minimum weight? If you want code to just work without labeling languages, highlight.js and its auto-detection is the least-effort choice. If you care most about the smallest possible runtime bundle and are happy to declare languages, Prism wins.
How much does fidelity matter? For complex, modern, or mixed-language code where mis-highlighting looks unprofessional, Shiki's VS Code grammars are in a class of their own.

These are not mutually exclusive. A common pattern is Shiki for the static docs and blog, with a runtime highlighter reserved for the one interactive playground that genuinely needs it. The upstream decision that matters most is the same as with your MDX pipeline: highlight where the code lives, not where it is convenient.

Which One for the Products You Sell

If you build and sell documentation site templates, blog starters, or component libraries and UI kits, the highlighter you wire in shapes how finished the product feels the moment a buyer opens it:

Docs, blog, and content templates: Shiki at build time gives editor-accurate code, dual light/dark themes, and no client JavaScript — exactly the polish and performance buyers use to judge a modern template.
Playground or live-editor templates: reach for a runtime highlighter — Prism for the lightest, most modular setup, or highlight.js when you want zero-config language detection.
Compatibility-first templates: if the buyer's stack already standardizes on Prism's plugins or highlight.js themes, matching that avoids a migration they did not ask for.

Whichever you ship, wire the highlighter in behind a single component or MDX config so a buyer can swap it, ship a sensible default theme, and make sure dark mode works out of the box. A flash of unstyled or mis-colored code is one of the first things that makes a template read as unfinished rather than production-ready.

The Bottom Line

highlight.js: the batteries-included runtime highlighter with automatic language detection and 190+ languages. The choice for dropping highlighting onto a page with the least setup.
Prism: the tiny, modular runtime tokenizer with the smallest bundle and the deepest plugin ecosystem. The choice when highlighting must ship to the browser and weight matters.
Shiki: the build-time highlighter with VS Code-accurate output, dual themes, and zero client JavaScript. The choice for static content where accuracy and performance win.

All three turn code into colored HTML; what differs is when and where. Pick build-time Shiki for content you control, and a runtime highlighter only where code appears after load. Ready to turn what you build into income? List your documentation or blog template on CodeCudos, see the wider picture in our best tech stack for web apps in 2026 guide, or compare the documentation frameworks your highlighted code will live in.

Shiki vs Prism vs highlight.js 2026: The Best Syntax Highlighter Compared