Lanexio Parser

Lanexio Parser is a modular parser framework for HTML, Markdown, JSON, YAML, and CSS. It produces a zero-copy flat AST backed by a single ArrayBuffer, parses any byte sequence without panicking or throwing, and passes 100% of the html5lib and CommonMark 0.31.2 test suites. Every grammar ships as a separate npm package so you pay only for what you use.

What’s included

• HTML: 100% html5lib conformance (5,199 tree-construction tests), all 23 insertion modes, adoption agency, foster parenting, foreign content.
• Markdown: 100% CommonMark 0.31.2 (652 specs) and 100% GFM (648 specs). Roundtrip serializer included.
• JSON: RFC 8259, complete JSONTestSuite corpus (311/311), strict accept/reject semantics with error-position reporting.
• YAML: YAML 1.2.2, 267/268 yaml-test-suite, structured flow collections, anchors/aliases/tags.
• CSS: CSS Syntax Level 3, full CourtBouillon corpus never-throw + error-detection agreement.
• Zero-copy flat AST: 16-byte nodes in preorder DFS, O(1) subtree skip, no per-node object allocation.
• Never-throw parse path: parse() never throws. Malformed input produces error nodes in the tree.
• Panic-free: any byte sequence of any length is accepted. Backed by fuzz harnesses and structural forward-progress guards.
• LexQuery: kind-name pattern queries with field and error modifiers.
• CLI: lanexio-parser parse/query/serialize with stdin support and strict invocation validation.

Quick start

Parse an HTML document:

import { parseHtml } from '@lanexio/parser-grammar-html';

const encoder = new TextEncoder();
const tree = parseHtml(encoder.encode('<h1>Hello</h1>'));

const cursor = tree.cursor();
visit: while (true) {
  console.log(cursor.current.kind, cursor.current.range);
  if (cursor.gotoFirstChild()) continue;
  while (!cursor.gotoNextSibling()) {
    if (!cursor.gotoParent()) break visit;
  }
}

Parse a Markdown document:

import { parseMarkdown } from '@lanexio/parser-grammar-markdown';

const encoder = new TextEncoder();
const tree = parseMarkdown(encoder.encode('# Hello\n\nA paragraph.'));

console.log(tree.nodeCount);   // number of nodes in the flat AST
console.log(tree.root.kind);   // numeric kind id for the document root

Installation Install Lanexio Parser with pnpm, npm, or yarn.

Quick Start Parse HTML and Markdown in five lines each.

Flat AST How the 16-byte node layout works.