val_latex

LaTeX math typesetting in pure Dart.

A TeX parser and layout engine with OpenType math fonts.
Runs anywhere Dart runs: the VM, Flutter on every platform, servers and the web.

🦋 Flutter widgets · 📦 pub.dev

✨ Why val_latex?

Pure Dart — no WebView, no JavaScript, no native code. The same engine runs in Flutter apps, on servers, in command-line tools and on the web.
TeX's own rules — layout follows the TeXbook's Appendix G and the OpenType MATH table of the font, so formulas are spaced the way LaTeX spaces them.
Broad coverage — 3,882 commands and 68 environments: amsmath, mathtools, the physics package, mhchem chemistry, siunitx units, diffcoeff, unicode-math names, text tables and lists.
Never throws on bad input — errors become nodes and diagnostics, and input that is still arriving (an LLM streaming a reply) renders as far as it goes.
Wraps to a width — breaks at relations and operators the way a person would, and re-breaks for a new width without laying out again.
Right-to-left math — Arabic notation, Arabic-Indic and Persian digits, mirrored operators and brackets.
Fast — about 4 µs to parse and 5 µs to lay out a typical formula on native code.

For Flutter, use val_latex_flutter. It adds the Math and MathText widgets on top of this package.

🛠️ Quick start

dart pub add val_latex

import 'package:val_latex/val_latex.dart';

final result = parseLatex(r'x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}');
final layout = layoutFormula(result);

print(layout.width);          // in em
print(result.diagnostics);    // problems, never an exception

layout.items is a render-agnostic display list — glyphs, rules, lines, paths and text runs, positioned in em. Draw it on any canvas, or use val_latex_flutter to draw it in Flutter.

📚 What it understands

Area	Highlights
Core LaTeX and AMS	fractions, roots, scripts and limits, accents, delimiters at every size, every math alphabet, colours (148 named)
Environments	`align`, `gather`, `multline`, `split`, `cases`, every matrix, `array` with rules and `\multicolumn`, `CD` and `tikzcd` diagrams, bussproofs proof trees, equation numbers and tags
Packages	amsmath, mathtools, physics, mhchem (`\ce`, `\pu`), siunitx, diffcoeff, commath, nccmath, empheq, esint, tensor, stmaryrd, wasysym, unicode-math names
Text	`\text` with math inside, `tabular` and booktabs tables, `itemize` / `enumerate` lists, justified paragraphs with hyphenation
Macros	`\def`, `\newcommand`, `\newenvironment`, `\NewDocumentCommand`, `\DeclareMathOperator`, `\DeclarePairedDelimiter`, TeX conditionals and registers, shared across formulas with one `newMacroTable()`
Unicode input	`α`, `∑`, `x²`, `a₁`, combining accents, Arabic letters and digits

Common package commands such as \abs, \dv, \sfrac and \celsius work without loading anything. LatexCatalog.instance lists everything val_latex understands.

📐 Layout and fonts

final layout = renderLatex(
  r'\sum_{k=1}^{n} k = \frac{n(n+1)}{2}',
  layoutOptions: const LayoutOptions(displayMode: true, maxWidth: 12),
);

Latin Modern Math is bundled, with STIX Two Math as the fallback for symbols it lacks. Any OpenType math font works: MathFont.fromBytes(bytes).
Variable fonts at any axis values: MathFont.fromBytes(bytes, variations: {'wght': 700}).
Line breaking — LayoutOptions.maxWidth; prepareFormula lays a formula out once and layoutAt(width) re-runs only the line breaker.
Right-to-left — LayoutOptions(mathDirection: MathDirection.rtl).
In the background — layoutInBackground lays a formula out in a worker isolate.

🔌 Streaming and text with formulas

parseLatex treats unfinished input (an open group, a half-typed command) as incomplete rather than wrong, and keeps node ids stable as more input arrives. MathScanner finds $…$ , $$…$$, $…$ and \[…\] formulas (and bare \begin{align}, cases, pmatrix…) in Markdown or chat text: prices stay text, code spans and blocks are skipped, and LLM output with doubled backslashes (\\[…\\]) still works.

🗣️ Speech, selection and source

toSpeech reads a formula aloud for screen readers, in English and Arabic (Spanish, French, German, Portuguese, Bengali and Hindi as drafts), at three levels of detail.
Every node carries its source span; hitTestLayout and selectionUnits map taps and selections back to the source.
toLatex writes a formula back as normalised LaTeX.

⚡ Performance

Measured on a MacBook (just bench), per formula of the coverage corpus:

	Native	JavaScript
Parse	4.5 µs	13 µs
Layout	5.4 µs	18 µs

Re-parsing and laying out a 160-character formula on every streamed character takes about 19 µs per update.

Built by Val

val_latex is part of Val, the live visual layer for AI agents.

💬 Community

Found a bug, or have an idea or feedback? Open an issue at github.com/useval/val_latex. If the package helps your project, consider giving it a like on pub.dev.

📄 License

BSD 3-Clause — see LICENSE. The bundled fonts keep their own licences: Latin Modern Math (GUST Font License) and STIX Two Math (SIL Open Font License), in fonts/. Work by others that val_latex contains is credited in THIRD_PARTY_NOTICES.md.