Istarion.Html 1.0.0-beta.1

Istarion.Html

A high-performance, DOM-less, low GC, streaming HTML parser and transformer library for .NET. Parse HTML via a SAX-style callback interface, decode entities, and transform HTML to formatted output or JSX (R.e("tag", props, ...)).

Features

• Streaming parser — Feed UTF-8 bytes or characters in chunks; no need to load the entire document into memory.
• SAX-style API — Implement IHtmlHandler to receive events: text, comments, elements (start/end), attributes, and script blocks.
• HTML entity decoding — Named and numeric entities via HtmlDecoder (e.g. &,  ,  ).
• Round-trip formatting — HtmlFormatter writes parsed HTML back out, preserving structure.
• HTML → JSX — JsxTransformer / JsxFormatter convert HTML to React-style JSX: R.e("div", { "class": "x" }, "text").
• Text rules — HtmlTextRules: known HTML5 tags, inline vs block, React-style whitespace normalization.
• ASP.NET Core integration — Implements IHtmlContent; use with HtmlEncoder and WriteTo(TextWriter, HtmlEncoder).
• Stream & writer adapters — HtmlStream and HtmlTextWriter for piping HTML through the parser into your handler.

Installation

dotnet add package Istarion.Html

Or in .csproj:

<PackageReference Include="Istarion.Html" Version="1.0.0" />

Requirements

• .NET 9.0 or .NET 10.0
• Microsoft.AspNetCore.App (for IHtmlContent and HTML encoding)

Getting started

Parse HTML with a custom handler

using Istarion.Html;

var writer = new StringWriter();
var handler = new HtmlFormatter(writer);
var parser = new HtmlParser(handler);

parser.FeedChars("<div>Hello</div>".AsSpan(), last: true);
// or: parser.FeedBytes(utf8Bytes, last: true);

writer.ToString(); // "<div>Hello</div>"

Transform HTML to JSX

using Istarion.Html;
using Microsoft.AspNetCore.Html;

string html = @"<div class=""container""><span>Hello</span></div>";
IHtmlContent source = new HtmlString(html);

using var output = new StringWriter();
var transformer = new JsxTransformer(output);
((IHtmlContent)transformer).WriteTo(output, HtmlEncoder.Default);

// output: R.e("div", { "class": "container" }, R.e("span", null, "Hello"))

Or from a string directly:

using var sw = new StringWriter();
var transformer = new JsxTransformer(sw);
transformer.Transform("<br/>");
// R.e("br", null)

Decode HTML entities

using Istarion.Html;

string decoded = HtmlDecoder.DecodeToString("& <  ".AsSpan());
// "& < \u00A0"

License

MIT. Copyright (c) 2026 Istarion Software Pty Ltd