What is Html Agility Pack?

Html Agility Pack (HAP) is a .NET code library that is used to parse HTML and XML documents. It is particularly useful for web scraping because it allows developers to navigate and manipulate HTML documents with ease, similar to what you can do with jQuery for client-side HTML manipulation. Html Agility Pack is often used in C# or other .NET languages to crawl web pages and extract data, manipulate HTML files, or clean up HTML content.

The library provides a way to create a document object model (DOM) structure from an HTML or XML string or file, which can then be queried and modified using XPath or LINQ queries. It is robust enough to handle malformed HTML as well, which is common on the web, making it very useful for scraping tasks where you have no control over the structure or validity of the HTML being processed.

Here's a simple example of how to use the Html Agility Pack in C# to load an HTML document and extract all the hyperlinks:

using System;
using System.Linq;
using HtmlAgilityPack;

class Program
{
    static void Main(string[] args)
    {
        // Create an instance of HtmlWeb class to load the document
        var web = new HtmlWeb();

        // Load the HTML document from a URL
        var document = web.Load("http://example.com");

        // Use XPath to find all anchor tags in the document
        var nodes = document.DocumentNode.SelectNodes("//a[@href]");

        // Iterate over all found nodes and print out the href attribute
        foreach (var node in nodes)
        {
            Console.WriteLine(node.Attributes["href"].Value);
        }
    }
}

To use Html Agility Pack, you typically need to install the package via NuGet Package Manager in Visual Studio or by using the NuGet CLI:

dotnet add package HtmlAgilityPack

Or for older projects that use the Package Manager Console:

Install-Package HtmlAgilityPack

Once installed, you can include the HtmlAgilityPack namespace in your project and start using its classes and methods to parse and manipulate HTML content.

Html Agility Pack offers a variety of features including:

• The ability to load HTML content from a string, file, or URL.
• A rich set of methods for querying and manipulating the DOM using XPath, LINQ, or traditional DOM navigation.
• Support for fixing up malformed HTML so that a valid DOM can be constructed from real-world web pages that often do not conform to HTML standards.
• Options to make changes to the loaded HTML document and then save the modified content to a file or stream.

Overall, Html Agility Pack is a powerful tool that provides .NET developers with a programmable interface for dealing with HTML that goes beyond simple pattern matching or string manipulation. It's widely used in web scraping, web testing, and any other scenarios where HTML content needs to be programmatically accessed and manipulated.