SeoAnalyzer 4.1.5

SeoAnalyzer

A lightweight, high-performance C# library designed for deep on-page SEO, Performance, and Security analysis. Built on top of AngleSharp, it fast-parses raw HTML or live URLs to deliver structured, production-ready diagnostic reports complete with automated audits, actionable fix recommendations, and segmented scores.

Installation

dotnet add package SeoAnalyzer

Usage

The library provides four entry points:

1. Seo.FromHtmlAsync(html, url): Audits SEO metrics on raw HTML, returning a SeoResult (includes Tech).
2. Seo.FromUrlAsync(url): Fetches a live URL and audits SEO, Performance, and Security, returning an AnalysisResult (includes Tech). Cookies set by the server are captured automatically.
3. Seo.AnalyzeAsync(pageContext): Runs a full audit from a pre-built PageContext, returning an AnalysisResult (includes Tech). Integrates with Playwright, Selenium, Puppeteer, etc.
4. Seo.DetectTechAsync(html, cookies?): Detects the technology stack only - no SEO/Performance/Security audits - returning a TechResult directly.

1. SEO Analysis from HTML String

using SeoAnalyzer;

var result = await Seo.FromHtmlAsync(html, url);

if (result != null)
{
    Console.WriteLine($"SEO Score: {result.Score}/100");
    foreach (var audit in result.Audits)
    {
        Console.WriteLine($"[{audit.Status}] {audit.Title}: {audit.Value}");
    }
}

2. Full URL Analysis (SEO, Performance & Security)

using SeoAnalyzer;

var result = await Seo.FromUrlAsync("https://www.amazon.com.br");

if (result != null)
{
    Console.WriteLine($"Overall Score: {result.TotalScore}/100");
    Console.WriteLine($"SEO: {result.Seo?.Score}/100 ({result.Seo?.TotalPassed} passed, {result.Seo?.TotalFailed} failed, {result.Seo?.TotalWarnings} warnings)");
    Console.WriteLine($"Performance: {result.Performance?.Score}/100");
    Console.WriteLine($"Security: {result.Security?.Score}/100");

    // Tech stack is always available directly
    Console.WriteLine($"CMS: {string.Join(", ", result.Tech?.Platforms ?? [])}");
    Console.WriteLine($"JS: {string.Join(", ", result.Tech?.JsFrameworks ?? [])}");
}

3. Technology Detection Only

Use Seo.DetectTechAsync when you only need the technology stack without running a full audit.

using SeoAnalyzer;

var tech = await Seo.DetectTechAsync(html);

Console.WriteLine($"Platforms : {string.Join(", ", tech.Platforms)}");
Console.WriteLine($"JS        : {string.Join(", ", tech.JsFrameworks)}");
Console.WriteLine($"CSS       : {string.Join(", ", tech.CssFrameworks)}");
Console.WriteLine($"reCAPTCHA : {tech.HasRecaptcha}");

4. Custom Page Context (Playwright, Selenium, etc.)

Use Seo.AnalyzeAsync(PageContext) when you already have the page loaded in a browser or from any external source. Pass Cookies to enable cookie-based platform detection - typically extracted from the browser's cookie store.

Playwright Example

using SeoAnalyzer;
using SeoAnalyzer.Models;
using Microsoft.Playwright;
using System.Text.Json;

var playwright = await Playwright.CreateAsync();
var browser = await playwright.Chromium.LaunchAsync();
var page = await browser.NewPageAsync();
var response = await page.GotoAsync("https://www.amazon.com.br");

var html = await page.ContentAsync();

// Extract real network metrics from the browser's Navigation Timing API
var timing = await page.EvaluateAsync<JsonElement>(@"() => {
    const e = performance.getEntriesByType('navigation')[0];
    return {
        dns: e.domainLookupEnd - e.domainLookupStart,
        tcp: e.connectEnd - e.connectStart,
        ttfb: e.responseStart - e.requestStart,
        download: e.responseEnd - e.responseStart,
        total: e.responseEnd - e.startTime
    };
}");

// Extract cookies from the browser context for platform detection
var browserCookies = await page.Context.CookiesAsync();
var cookieString = string.Join("; ", browserCookies.Select(c => $"{c.Name}={c.Value}"));

// Convert Playwright response headers to HttpResponseHeaders
var httpResponse = new HttpResponseMessage();
foreach (var header in response!.Headers)
    httpResponse.Headers.TryAddWithoutValidation(header.Key, header.Value);

var result = await Seo.AnalyzeAsync(new PageContext
{
    Html = html,
    Url = page.Url,
    Metrics = new NetworkPerformanceMetrics
    {
        DnsLookupMs = timing.GetProperty("dns").GetDouble(),
        TcpConnectionMs = timing.GetProperty("tcp").GetDouble(),
        TtfbMs = timing.GetProperty("ttfb").GetDouble(),
        ContentDownloadMs = timing.GetProperty("download").GetDouble(),
        TotalNetworkTimeMs = timing.GetProperty("total").GetDouble()
    },
    ResponseHeaders = httpResponse.Headers,
    Cookies = cookieString  // cookies from the browser's cookie store
});

Console.WriteLine($"Score: {result?.TotalScore}/100");

await browser.CloseAsync();

What is Analyzed?

1. Search Engine Optimization (SEO) - FromHtmlAsync, FromUrlAsync, AnalyzeAsync

• Metadata: Title, Description, Canonical Tag, Robots, Viewport, Charset, Lang Attribute, and Favicon.
• Content & Structure: Single H1 Tag, Heading Hierarchy (fails if no H2 or H3 tags are present), and Common Keywords Presence.
• Links: Internal vs External Links ratio and Empty Anchor Text.
• Images: Missing Alt Text (details return a list of image URLs).
• Social & Structured Data: Open Graph (Facebook/LinkedIn), Twitter Cards, and JSON-LD/Microdata Structured Data.
• Technical SEO: Robots.txt, XML Sitemap, and Google Tag Manager (Scripts, Noscripts, dataLayer).

2. Technology Detection - all entry points, also standalone via DetectTechAsync

Available as a dedicated TechResult object on every result and via Seo.DetectTechAsync.

• CMS / Site Builder: WordPress, Wix, Shopify, Squarespace, Webflow, Joomla, Drupal, Umbraco, TYPO3, Blogger, Weebly, Jimdo, GoDaddy Builder, Hostinger, Duda, NuvemShop, LojaIntegrada, Tray, Hotmart, Kiwify, Cartpanda.
• JavaScript Frameworks: React, Next.js, Vue.js, Nuxt.js, Angular, Svelte, Ember.js, Backbone.js, Alpine.js, HTMX, jQuery, Stimulus, Lit.
• CSS Frameworks / Libraries: Bootstrap, Tailwind CSS, Bulma, Foundation, Materialize CSS, Semantic UI.
• reCAPTCHA: Detects Google reCAPTCHA v2, v3, and Enterprise via script URLs and DOM signals.

2. Performance - FromUrlAsync, AnalyzeAsync

• Detailed Network Connection Timings (requires Metrics in PageContext):
  • DNS Lookup Time
  • TCP Connection Time
  • Server Response Time (TTFB)
  • Content Download Time
  • Total Network Time
• DOM Size: Checks if the document exceeds the Lighthouse threshold (up to 1500 elements).
• Resource Hints: Checks for <link rel="preconnect"> or dns-prefetch optimization tags.
• Minification Check: Audits if external stylesheets and scripts are properly minified (.min.css / .min.js).
• HTML Size: Validates whether the HTML size is within acceptable limits (up to 600 KB).
• Image Dimensions & Delivery: Image Width/Height (CLS checks), Lazy Loading presence, and Modern Image Formats (WebP/AVIF).

3. Security - FromUrlAsync, AnalyzeAsync

• HTTPS Usage: Validates whether the website utilizes SSL/TLS transport protocol.
• Insecure Resources (Mixed Content): Ensures that an HTTPS page does not fetch insecure HTTP assets.
• Secure Password Forms: If a password input field exists, ensures that the hosting page and the submitting form action use secure HTTPS endpoints.
• Content Security Policy (CSP): Audits for the presence of a CSP declaration meta tag.
• HTTP Security Headers (requires ResponseHeaders in PageContext): Audits response headers for security protection configurations (Strict-Transport-Security, X-Frame-Options, X-Content-Type-Options, and Referrer-Policy).
• TLS Protocol Version: Performs a secure connection test handshake to verify the server uses modern TLS 1.2 or 1.3 protocol.
• External Link Target Security: Audits target="_blank" links for missing rel="noopener" or rel="noreferrer" attributes.

Response Structure

Data Models

SeoResult

AnalysisResult

CategorySummary

SeoAudit

PageContext

AuditStatus Values

Structured Details Types

When an audit fails or requires deeper diagnostics, the Details property contains one of the following concrete types depending on the audit:

• HeadingAuditItem: Contains the hierarchy and count of heading tags (H1 to H6).
• TagAuditItem: Lists obsolete or deprecated HTML tags found within the document.
• AttributeAuditItem: Lists deprecated HTML attributes used in the document markup.
• List<string>: A flat list of paths, URIs, header keys, or detected technology names (e.g., image URLs missing alt/dimensions, scripts, unminified resources, risky external links, or detected frameworks/platforms).

TechResult

Requirements

.NET 9.0 SDK or higher.