How Does Shiki Achieve Accurate and Beautiful Syntax Highlighting?

Shiki produces accurate, beautiful syntax highlighting by using the same TextMate grammars and highlighting engine as VS Code, then generating static HTML at build time instead of highlighting in the browser. That combination is why its output looks like the editor you already use, and why it adds no runtime highlighting cost to your page. The trade-off is that highlighting happens ahead of time, so themes and languages are resolved when you generate the HTML, not when a reader opens the page.

The two mechanisms behind Shiki's output

Shiki's result comes from two separate decisions that reinforce each other:

1. Grammar source: It uses TextMate grammars, the same grammar format that powers VS Code's tokenization.
2. Execution model: It runs that tokenization ahead of time and emits HTML, rather than shipping a highlighter to the browser.

Each one solves a different problem. The grammar choice determines what the highlighting looks like; the execution model determines when and where the work happens.

Why the highlighting matches VS Code

TextMate grammars are rule sets that describe how to break a language into tokens — keywords, strings, comments, function names, and so on. Because Shiki consumes the same grammar definitions VS Code uses, the token boundaries it produces are the same ones VS Code produces.

The site states this directly: Shiki is "TextMate grammar powered, same engine as your VS Code." It also notes that it "Improves with VS Code" — meaning grammar fixes and language updates that land in VS Code flow into Shiki's output rather than requiring a separate, hand-maintained set of rules.

The practical consequence: if a language highlights a certain way in your editor, it highlights that way in your generated HTML. You are not comparing two independently written highlighters and hoping they agree.

What "accurate" means here

Accuracy in this context is about token classification, not aesthetics. A grammar that misreads a template literal, a regex, or an embedded language will color the wrong spans. Reusing VS Code's grammars means those edge cases are handled by the same rules that already handle them in the editor, including nested and embedded languages.

Why there is no runtime cost

Shiki's "Zero Runtime" property means the highlighting logic does not execute in the reader's browser. The tokenization runs when you build or render your site, and the output is static HTML with the colors already applied.

This matters for three reasons:

• No highlighter JavaScript to download or parse for the purpose of coloring code.
• No flash of unstyled or re-highlighted code, because the colored markup is present in the initial HTML.
• Predictable output, since the same input and configuration produce the same markup every time.

The cost moves to your build step. If you highlight a large number of code blocks or many languages, that work happens during generation rather than on each page view.

A concrete example

Suppose you publish a blog post containing a TypeScript snippet with an embedded GraphQL string. With a browser-side highlighter, the page loads plain text, the highlighter script runs, and the code is colored afterward — and any language or grammar the highlighter does not support stays uncolored. With Shiki, the build step tokenizes the snippet using the TypeScript and GraphQL grammars, and the served HTML already contains the correctly colored spans. The reader's browser does no highlighting work at all.

Customization and output format

Shiki is described as customizable and as ESM & Universal. In practice this means you can choose themes and configure how the highlighted output is rendered, and you can use it across different build setups rather than being locked to one bundler or framework.

Because highlighting is resolved at generation time, your theme and language choices are part of the build configuration. Changing a theme means regenerating the output, not toggling something at runtime.

When this approach fits — and when it does not

The core decision is simple: if your code samples are known at build time and you want editor-identical coloring with no client-side highlighting, Shiki's grammar-plus-static-output design is built for exactly that. If your code is generated dynamically per request, you are moving the same highlighting step to a different point in the pipeline.