A TextMate-grammar syntax highlighter for Scala.

Why highlighter

highlighter turns source code into highlighted output using TextMate grammars — the same .tmLanguage.json files that drive VS Code. Point it at a grammar, hand it a snippet, and it gives you back highlighted HTML, or the raw tokens to render however you like.

import io.github.edadma.highlighter.*

val Right(hl) = Highlighter.fromJson(grammarJson, InlineMode(Theme.OneDark)): @unchecked
println(hl.highlight("val x = 42"))
// <span style="color:#c678dd">val</span> x = <span style="color:#d19a66">42</span>

The grammar engine is a full regex state machine — begin/end spans, captures, repository includes, $self references, cycle detection — running on a pure-Scala port of Oniguruma, so the same grammars work identically on every platform, with no native dependency.

A Scala snippet, highlighted by this site at build time from highlighter’s own Scala grammar:

// quicksort
def sort(xs: List[Int]): List[Int] = xs match
  case Nil => Nil
  case pivot :: rest =>
    val (less, more) = rest.partition(_ < pivot)
    sort(less) ++ (pivot :: sort(more))

val nums = List(5, 2, 8, 1, 9)
println(sort(nums))  // List(1, 2, 5, 8, 9)

What’s here

• Getting Started — add the dependency and highlight your first snippet.
• Guide — loading grammars, the HTML render modes, themes, and consuming tokens directly.

What it does

• TextMate grammar engine — match and begin/end patterns, captures, contentName, repository rule sets, #rule / $self includes, with cycle detection.
• Two HTML render modes — CSS classes with a configurable prefix, or inline style colours from a theme.
• Built-in themes — OneDark, OneLight, and Monokai, or your own colour scheme.
• Tokens, not just HTML — take List[List[Token]] (one list per source line) and render to a PDF, a terminal, or a GUI against your own palette.
• Three platforms — the JVM, Scala.js, and Scala Native, all from one pure-Scala codebase.