TagChecker 1.0.2

.NET 8.0

dotnet add package TagChecker --version 1.0.2

NuGet\Install-Package TagChecker -Version 1.0.2

This command is intended to be used within the Package Manager Console in Visual Studio, as it uses the NuGet module's version of Install-Package.

<PackageReference Include="TagChecker" Version="1.0.2" />

For projects that support PackageReference, copy this XML node into the project file to reference the package.

<PackageVersion Include="TagChecker" Version="1.0.2" />
                    

                            Directory.Packages.props

<PackageReference Include="TagChecker" />
                    

                            Project file

For projects that support Central Package Management (CPM), copy this XML node into the solution Directory.Packages.props file to version the package.

paket add TagChecker --version 1.0.2

The NuGet Team does not provide support for this client. Please contact its maintainers for support.

#r "nuget: TagChecker, 1.0.2"

#r directive can be used in F# Interactive and Polyglot Notebooks. Copy this into the interactive tool or source code of the script to reference the package.

#:package TagChecker@1.0.2

#:package directive can be used in C# file-based apps starting in .NET 10 preview 4. Copy this into a .cs file before any lines of code to reference the package.

#addin nuget:?package=TagChecker&version=1.0.2
                    

                            Install as a Cake Addin

#tool nuget:?package=TagChecker&version=1.0.2
                    

                            Install as a Cake Tool

The NuGet Team does not provide support for this client. Please contact its maintainers for support.

TagChecker

A .NET library for validating HTML tag structure and reporting parse errors with line/column positions.

Supported target frameworks: net8.0, net9.0, net10.0.

Features

Validates start/end tag matching and nesting order
Detects missing start or end tags
Parses attributes and detects malformed attribute syntax
Handles HTML comments (``) and DOCTYPE (<!DOCTYPE ...>)
Handles raw-content tags (<script>, <style>) without false parsing on < inside content
Validates HTML void-element rules with strict behavior
Returns structured error details (ErrorCode, LineNumber, Position)

Clone, Build, and Test

git clone https://github.com/foman/TagChecker.git
cd TagChecker
dotnet restore TagChecker.sln
dotnet build TagChecker.sln -c Release
dotnet test TagChecker.sln -c Release

Install from NuGet

dotnet add package TagChecker

Or in .csproj:

<ItemGroup>
  <PackageReference Include="TagChecker" Version="1.0.0" />
</ItemGroup>

Quick Start

using TagChecker;

var html = "<html><body><div class='x'>Hello</div></body></html>";
var (ok, error) = HtmlTagChecker.Validate(html);

if (ok)
{
    Console.WriteLine("HTML is valid");
}
else
{
    Console.WriteLine($"Error: {error.ErrorCode} at line {error.LineNumber}, col {error.Position}");
}

API

`HtmlTagChecker.Validate(string content, ParserOptions? options = null)`

Returns:

(bool succeed, TagError tagError)

succeed: true when validation passes
tagError: null on success; populated on failure

`ParserOptions`

new ParserOptions
{
    TagNamePatternStrict = true
}

TagNamePatternStrict = false (default): compatibility mode
TagNamePatternStrict = true: enforces strict tag-name pattern:
- first character must be a letter (A-Z / a-z)
- remaining characters can be letters, digits, or hyphen (-)

Behavior Notes

Void elements

TagChecker currently uses strict void-element behavior:

<img /> is valid
<img> triggers VoidElementNotSelfClosed (strict XML-like rule)
</img> triggers VoidElementClosed

Void-element set: area, base, br, col, embed, hr, img, input, link, meta, param, source, track, wbr

Script/style content

For <script> and <style>, content is treated as raw text until matching closing tags. This avoids incorrect parsing when the content contains < characters.

Error Codes

TagNotClosed: Missing closing > for a tag
NoStartTagFound: Closing tag has no matching opener
NoEndTagFound: Opening tag has no matching closer
InvalidTag: Invalid tag structure
InvalidTagName: Invalid tag name
InValidCloseTag: Invalid closing tag format
InvalidAttribute: Invalid attribute syntax
InvalidAttributeName: Invalid attribute name
AttributeNotClosed: Attribute value quote not closed
VoidElementClosed: Void element incorrectly closed using </...>
VoidElementNotSelfClosed: Void element not self-closed

Examples

Success

var (ok, err) = HtmlTagChecker.Validate("<div><span>Hello</span></div>");
// ok == true
// err == null

Missing end tag

var (ok, err) = HtmlTagChecker.Validate("<div><span>Hello</div>");
// ok == false
// err.ErrorCode == HtmlParseErrorCode.NoStartTagFound (mismatched close)

Strict tag-name validation

var options = new ParserOptions { TagNamePatternStrict = true };
var (ok, err) = HtmlTagChecker.Validate("<1bad></1bad>", options);
// ok == false
// err.ErrorCode == HtmlParseErrorCode.InvalidTagName

Publish to NuGet (lightweight script)

Use the lightweight helper script:

# Dry run (test + pack only)
./scripts/nuget-publish.sh --version 0.2.0 --dry-run

# Real publish
NUGET_API_KEY=*** ./scripts/nuget-publish.sh --version 0.2.0

Optional flags:

--skip-tests: skip unit tests before packing
--source <url>: custom NuGet source

Publish via GitHub Release (GitHub Actions)

publish.yaml is configured to publish when a GitHub Release is published.

Trigger: release.published
Version source: release tag (e.g. v0.2.0 → package version 0.2.0)
Required secret: NUGET_API_KEY

Quick flow:

Push tag, e.g. v0.2.0
Create a GitHub Release for that tag
GitHub Actions runs build/test/pack/publish automatically

Roadmap (next)

Add parser modes: strict (current) vs lenient HTML5 void-element behavior
Improve diagnostics with source snippets around error locations
Add performance benchmarks for large files and deep nesting

Product	Compatible and additional computed target framework versions.
.NET	net8.0 is compatible. net8.0-android was computed. net8.0-browser was computed. net8.0-ios was computed. net8.0-maccatalyst was computed. net8.0-macos was computed. net8.0-tvos was computed. net8.0-windows was computed. net9.0 is compatible. net9.0-android was computed. net9.0-browser was computed. net9.0-ios was computed. net9.0-maccatalyst was computed. net9.0-macos was computed. net9.0-tvos was computed. net9.0-windows was computed. net10.0 is compatible. net10.0-android was computed. net10.0-browser was computed. net10.0-ios was computed. net10.0-maccatalyst was computed. net10.0-macos was computed. net10.0-tvos was computed. net10.0-windows was computed.

Product

.NET

Compatible target framework(s)

Included target framework(s) (in package)

Learn more about Target Frameworks and .NET Standard.

net10.0
- No dependencies.
net8.0
- No dependencies.
net9.0
- No dependencies.

NuGet packages

This package is not used by any NuGet packages.

GitHub repositories

This package is not used by any popular GitHub repositories.

Version	Downloads	Last Updated
1.0.2	104	2/15/2026
1.0.2-alpha	92	2/15/2026
1.0.1	101	2/15/2026
1.0.0	106	2/15/2026