syntect

name	syntect
description	Expert knowledge for syntax highlighting in Rust with syntect — Sublime Text syntax definitions and TextMate themes producing ANSI-terminal and HTML output, including TypeScript support and modern themes. Use when highlighting code for terminal or HTML output, loading custom syntaxes or themes, or troubleshooting highlighting performance.
last_updated	"2025-12-24T00:00:00.000Z"
hash	285587f8ac19de6c

Syntect

Syntect is a high-performance syntax highlighting library for Rust that uses Sublime Text syntax definitions (.sublime-syntax) and TextMate themes (.tmTheme). It's the industry standard for Rust-based syntax highlighting, used in bat, delta, and various static site generators.

Core Principles

• Two-stage pipeline: Parsing (text → scopes) then Highlighting (scopes → styles)
• Line-by-line processing: Process code incrementally for memory efficiency
• Pre-load defaults: Use SyntaxSet::load_defaults_newlines() and ThemeSet::load_defaults() for convenience
• Binary dumps for production: Compile syntaxes/themes to binary at build time for <5ms startup
• ANSI for terminals: Use as_24_bit_terminal_escaped() for 24-bit color terminal output
• HTML has two modes: Inline styles (self-contained) or CSS classes (better performance/theme switching)
• Streaming for large files: Use HighlightFile for memory-efficient file processing
• Always reset terminal: Print \x1b[0m after ANSI output to reset colors

Setup

[dependencies]
syntect = "5.2"

Quick Reference

Terminal Output (ANSI Escape Codes)

use syntect::easy::HighlightLines;
use syntect::parsing::SyntaxSet;
use syntect::highlighting::ThemeSet;
use syntect::util::{as_24_bit_terminal_escaped, LinesWithEndings};

let ps = SyntaxSet::load_defaults_newlines();
let ts = ThemeSet::load_defaults();
let syntax = ps.find_syntax_by_extension("rs").unwrap();
let mut h = HighlightLines::new(syntax, &ts.themes["base16-ocean.dark"]);

let code = "fn main() {}\n";
for line in LinesWithEndings::from(code) {
    let ranges = h.highlight_line(line, &ps).unwrap();
    print!("{}", as_24_bit_terminal_escaped(&ranges[..], false));
}
println!("\x1b[0m"); // Reset terminal color

HTML Output (Inline Styles)

use syntect::html::highlighted_html_for_string;
use syntect::parsing::SyntaxSet;
use syntect::highlighting::ThemeSet;

let ps = SyntaxSet::load_defaults_newlines();
let ts = ThemeSet::load_defaults();
let syntax = ps.find_syntax_by_extension("rs").unwrap();
let theme = &ts.themes["base16-ocean.dark"];

let html = highlighted_html_for_string("let x = 5;", &ps, syntax, theme).unwrap();
// Generates <pre style="..."> with nested <span> tags with inline colors

HTML Output (CSS Classes)

use syntect::html::{ClassedHTMLGenerator, ClassStyle};
use syntect::parsing::SyntaxSet;
use syntect::util::LinesWithEndings;

let ps = SyntaxSet::load_defaults_newlines();
let syntax = ps.find_syntax_by_extension("rs").unwrap();
let mut html_gen = ClassedHTMLGenerator::new_with_class_style(
    syntax, &ps, ClassStyle::Spaced
);

for line in LinesWithEndings::from("fn main() {}") {
    html_gen.parse_html_for_line_which_includes_newline(line).unwrap();
}

let html = html_gen.finalize();
// Output: <span class="source rust"><span class="meta function rust">...</span></span>

Topics

Output Targets

• Terminal/Console Output - ANSI escape codes for CLI tools
• HTML Generation - Inline styles and CSS class approaches
• Large File Handling - Streaming with HighlightFile

Language Support

• TypeScript Grammar - Loading TypeScript syntax definitions and using the two-face crate

Optimization

• Binary Dumps - Pre-compile syntaxes/themes for fast startup, modern themes integration

Common Patterns

Finding a Syntax by Extension

let ps = SyntaxSet::load_defaults_newlines();
let syntax = ps.find_syntax_by_extension("rs").unwrap();

Finding a Syntax by First Line (Shebang)

let syntax = ps.find_syntax_by_first_line("#!/usr/bin/env python3");

Available Default Themes

Common themes in ThemeSet::load_defaults():

• base16-ocean.dark
• base16-ocean.light
• InspiredGitHub
• Solarized (dark)
• Solarized (light)

When to Use Syntect

Use Case	Choose Syntect When
CLI tools	Need fast, accurate terminal highlighting
Static site generators	Generating HTML from code blocks
Documentation tools	Rendering code examples in docs
Code viewers	Displaying source code with syntax colors

Alternatives:

• Tree-sitter: For semantic analysis, ASTs, or IDE features (slower for pure highlighting)
• Pygments (Python): For Python-based tools (much slower, requires Python bridge)

Resources

• Crates.io
• Documentation
• GitHub