NkkinParser 1.0.0

NkkinParser 🚀

The fastest, lowest-allocation HTML5 parser in .NET

Faster than AngleSharp on parsing and selection, dramatically faster than HtmlAgilityPack on selection • SIMD-accelerated • Full tolerant HTML5 parsing • CSS selector engine with selector lists, nth-child formulas, and more

NkkinParser is a high-performance HTML/CSS parser built for .NET 10 from the ground up, using:

• ReadOnlySpan<char> + unsafe code in hot paths
• AVX2/AVX-512 SIMD for tag/text/attribute scanning
• Arena-backed allocation, with optional opt-in object pooling for repeated parse/dispose cycles
• Compiled, cached selectors with ID/class/tag indexing
• Streaming pull parser for large documents
• HtmlLoader.LoadAsync(url) for parsing directly from a URL with auto-decompression

No external dependencies.

Performance Benchmarks

Measured with the benchmark suite in this repo (NkkinParser.Benchmarks/) — synthetic generated documents, not real-world pages. Run with dotnet run -c Release --project NkkinParser.Benchmarks/NkkinParser.Benchmarks.csproj -- * to reproduce on your own hardware; full methodology (equal work per competitor, parse cost excluded from selector timings for all libraries, etc.) is documented in the benchmark source files.

The numbers below are from a short, low-iteration run (--job short, N=3) on an Intel Core i3-8100 (4 cores), .NET 10.0.10 — good enough to sanity-check relative performance, not publication-grade statistics (see the wide error margins). Re-run with the default job for tighter confidence intervals.

Parsing (ParsingBenchmark, per-operation time to parse three documents of ~10KB/100KB/1MB combined):

CSS selector queries (SelectorBenchmark, "a[href], div, span.class-name, #search" against a pre-parsed 5000-element document; parse cost excluded from all three):

Streaming vs. sync parse (StreamingBenchmark, 10,000-element document):

ParseAsync still parses the whole document up front and then walks it asynchronously (Task.Yield per node) — it trades throughput for interleaving/backpressure, it isn't a lower-latency or lower-allocation path.

Usage Examples

Full DOM Parsing

using NkkinParser;

var html = await File.ReadAllTextAsync("page.html");
using var parser = new HtmlParser(html);
var document = parser.Parse();

var images = document.QuerySelectorAll("img[src]");
foreach (var img in images)
{
    var src = img.Attributes.Get("src");
    Console.WriteLine(src);
}

Scoped queries on an element

var article = document.QuerySelector("article");
var links = article?.QuerySelectorAll("a[href]");

Supported CSS selectors

Type/universal/#id/.class selectors, attribute selectors ([attr], [attr=val], [attr=val i] case-insensitive), combinators ( , >, +, ~), selector lists (a, b), and pseudo-classes: :first-child, :last-child, :first-of-type, :last-of-type, :nth-child(an+b), :nth-last-child(an+b), :nth-of-type(an+b), :nth-last-of-type(an+b), :not(...).

Test suite

87 tests covering tokenization, tree construction (including the adoption agency algorithm for misnested tags), selector matching, encoding detection, and streaming. Run with dotnet test.