scah (scan HTML)

World's fastest CSS Selector.

CSS selectors meet streaming XML/HTML parsing. Filter StAX events and build targeted DOMs without loading the entire document.

What is scah?

scah is a high-performance parsing library that bridges the gap between SAX/StAX streaming efficiency and DOM convenience. Instead of loading an entire document into memory or manually tracking parser state, you declare what you want with CSS selectors; the library handles the streaming complexity and builds a targeted DOM containing only your selections.

• Streaming core: Built on StAX; constant memory regardless of document size
• Familiar API: CSS selectors (including combinators like >, , + (coming soon), ~ (coming soon))
• Multi-language: Rust core with Python and TypeScript/JavaScript bindings
• Composable queries: Chain selections and nest them with closures for structured querying; not only more efficient than flat filtering, but a fundamentally better pattern for extracting hierarchical data relationships

Quick Start

Rust

# Cargo.toml
[dependencies]
scah = "0.0.13"

Basic usage

use scah::{Query, Save, parse};

let html = r#"<ul><li><a href="/one">One</a></li><li><a href="/two">Two</a></li></ul>"#;

let queries = &[Query::all("a[href]", Save::all()).build()];
let store = parse(html, queries);

for a in store.get("a[href]").unwrap() {
    let href = a.attribute(&store, "href").unwrap();
    let text = a.text_content(&store).unwrap_or_default();
    println!("{text}: {href}");
}
// Output:
//   One: /one
//   Two: /two

Structured querying with .then()

Instead of flat filtering, nest queries with closures. Child queries only run within the context of their parent match:

use scah::{Query, Save, parse};

let query = Query::all("main > section", Save::all())
    .then(|section| [
        section.all("> a[href]", Save::all()),
        section.all("div a", Save::all()),
    ])
    .build();

let store = parse(html, &[query]);

// Access nested results through parent elements
for section in store.get("main > section").unwrap() {
    println!("Section: {}", section.inner_html.unwrap_or(""));

    if let Some(links) = section.get(&store, "> a[href]") {
        for link in links {
            println!("  Direct link: {}", link.attribute(&store, "href").unwrap());
        }
    }
}

Save options

Control what data is captured per selector:

Supported CSS selector syntax

Full API documentation: docs.rs/scah

Benchmarks

Python

pip install -U scah

from scah import Query, Save, parse 

query = Query.all("main > section", Save.all())
    .then(lambda section: [
        section.all("> a[href]", Save.all()),
        section.all("div a", Save.all()),
    ])
    .build()

store = parse(html, [query])

Benchmark's

Real Html BenchMark (html.spec.whatwg.org) (select all a tags):

Synthetic Html BenchMark (select all a tags):

Typescript / Javascript

npm install scah@npm:@zacharymm/scah

import { Query, parse } from 'scah';

const query = Query.all('main > section', { innerHtml: true, textContent: true })
  .then((p) => [
    p.all('> a[href]', { innerHtml: true, textContent: true }),
    p.all('div a', { innerHtml: true, textContent: true }),
  ])
  .build();

const store = parse(html, [query]);