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All lessons in Technical SEO Auditing Lesson 7.5 of 84

Module 1: Introduction to Technical SEO Auditing

  1. 1.1What Is a Technical SEO Audit?
  2. 1.2Technical SEO Audit vs. General SEO Audit
  3. 1.3When Should You Audit a Website?
  4. 1.4Types of Technical SEO Issues
  5. 1.5Defining Audit Scope and Objectives

Module 2: Website Crawling and URL Discovery

  1. 2.1How SEO Crawlers Discover URLs
  2. 2.2Configuring a Website Crawl
  3. 2.3Crawl Scope, Limits, and Exclusions
  4. 2.4Internal Links and Crawl Depth
  5. 2.5Orphan Pages and URL Discovery
  6. 2.6Crawl Data vs. Search Engine Data
  7. 2.7Identifying Crawl Coverage Gaps

Module 3: HTTP Status Codes and Redirect Auditing

  1. 3.1Understanding HTTP Status Codes
  2. 3.2Finding 4xx Errors and Broken Links
  3. 3.3Identifying 5xx Server Errors
  4. 3.4Redirect Chains and Redirect Loops
  5. 3.5Internal Links to Redirected URLs
  6. 3.6301 vs. 302 Redirects
  7. 3.7Auditing 404 Pages and Soft 404s

Module 4: Crawlability and Indexability Auditing

  1. 4.1Crawling vs. Indexing
  2. 4.2Robots.txt Audit
  3. 4.3Meta Robots and X-Robots-Tag
  4. 4.4Noindex and Canonical Conflicts
  5. 4.5XML Sitemap Validation
  6. 4.6Canonical URL Auditing
  7. 4.7Identifying Indexability Conflicts
  8. 4.8Comparing Crawl Data with Google Search Console

Module 5: URL Structure and Duplicate Content Issues

  1. 5.1URL Structure and Normalization
  2. 5.2Duplicate URLs and Duplicate Pages
  3. 5.3HTTP vs. HTTPS and Hostname Variations
  4. 5.4Trailing Slashes and URL Parameters
  5. 5.5Pagination and Faceted Navigation
  6. 5.6Canonicalization Strategies
  7. 5.7Internal Linking to Preferred URLs

Module 6: Technical On-Page Auditing

  1. 6.1Missing and Duplicate Title Tags
  2. 6.2Missing and Duplicate Meta Descriptions
  3. 6.3Missing, Duplicate, and Multiple H1 Headings
  4. 6.4Heading Hierarchy and HTML Structure
  5. 6.5Missing Image Alt Attributes
  6. 6.6Internal Link and Anchor Text Issues
  7. 6.7Empty, Thin, and Near-Duplicate Pages
  8. 6.8Auditing HTML Metadata at Scale

Module 7: Website Performance and Core Web Vitals

  1. 7.1Core Web Vitals: LCP, INP, and CLS
  2. 7.2Lab Data vs. Field Data
  3. 7.3Identifying Slow Pages
  4. 7.4Image and Resource Optimization Opportunities
  5. 7.5JavaScript and CSS Performance
  6. 7.6Mobile Usability and Responsive Rendering
  7. 7.7Prioritizing Performance Fixes

Module 8: JavaScript SEO and Rendering

  1. 8.1How Search Engines Process JavaScript
  2. 8.2HTML Source vs. Rendered HTML
  3. 8.3Client-Side vs. Server-Side Rendering
  4. 8.4JavaScript-Generated Content and Links
  5. 8.5Rendering Failures and Missing Content
  6. 8.6Lazy Loading and Crawl Accessibility
  7. 8.7Diagnosing JavaScript SEO Problems

Module 9: Structured Data and Schema Auditing

  1. 9.1Structured Data and Schema.org Basics
  2. 9.2JSON-LD and Structured Data Formats
  3. 9.3Finding Structured Data Across a Website
  4. 9.4Detecting Invalid or Incomplete Markup
  5. 9.5Schema Validation and Rich Result Eligibility
  6. 9.6Conflicting or Duplicate Structured Data
  7. 9.7Prioritizing Schema Fixes

Module 10: Analyzing Audit Data and Prioritizing Issues

  1. 10.1Reading Crawl Reports and Exports
  2. 10.2Grouping URLs by Issue Type
  3. 10.3Identifying Root Causes vs. Symptoms
  4. 10.4Evaluating Severity, Impact, and Effort
  5. 10.5Separating Sitewide and Isolated Issues
  6. 10.6Identifying False Positives
  7. 10.7Building an Actionable Issue Register

Module 11: Technical SEO Audit Reporting

  1. 11.1Structuring a Technical SEO Audit Report
  2. 11.2Documenting Evidence and Affected URLs
  3. 11.3Writing Developer-Ready Recommendations
  4. 11.4Mapping Issues to Business and Search Impact
  5. 11.5Creating a Prioritized Remediation Roadmap
  6. 11.6Presenting Findings to Stakeholders
  7. 11.7Tracking Fixes and Ownership

Module 12: Fix Verification and Technical QA

  1. 12.1Re-Crawling After Fixes
  2. 12.2Comparing Before-and-After Crawl Results
  3. 12.3Verifying Redirects, Canonicals, and Indexability
  4. 12.4Detecting Regressions and Newly Introduced Issues
  5. 12.5Testing Website Changes Before Deployment
  6. 12.6Confirming Fixes with Search Console and Other Evidence
  7. 12.7Closing Audit Findings and Recording Results

JavaScript and CSS Performance

In this lesson

  • How CSS and JavaScript block rendering
  • How unused code and long tasks affect LCP and INP
  • How to measure third-party script impact
  • Which fixes to recommend to developers

Short answer

JavaScript and CSS slow pages when they block rendering, ship unused code, or run long tasks on the main thread. Audit them with Lighthouse diagnostics for render-blocking resources, unused CSS and JavaScript, total blocking time, and third-party impact, then recommend deferring scripts, removing unused code, and limiting heavy third-party tags.

A Quezon City clinic’s site loaded 41 JavaScript files: a page builder, two sliders, a chat widget, three analytics tags, a pop-up tool, and a booking plugin used on only one page. On a mid-range Android phone, tapping the menu took nearly a second to respond.

How CSS and JavaScript slow pages

  • Render blocking: CSS and synchronous scripts in the head delay first paint and LCP.
  • Unused code: whole libraries loaded for one feature, or every plugin’s files loaded on every page.
  • Long tasks: heavy scripts keep the main thread busy, so taps wait. This hurts INP.
  • Third parties: chat, ads, heatmaps, and social embeds often cost more than your own code.

What to check

In Lighthouse (PageSpeed Insights lab section), review:

  1. Eliminate render-blocking resources
  2. Reduce unused JavaScript and unused CSS
  3. Total Blocking Time and long main-thread tasks
  4. Reduce the impact of third-party code
  5. Minify CSS and JavaScript

Repeat on each template, since plugins often load per page type.

Recommendations developers can act on

  • Add defer to non-critical scripts.
  • Inline critical CSS, load the rest asynchronously.
  • Load plugin files only on pages that use them.
  • Break up long tasks and delay non-essential widgets until user interaction.
  • Remove unused tags from Tag Manager.

Practice: what does this mainly hurt?

Sort each item into the right group.

  • Large CSS file blocking first paint

  • Chat widget running long tasks on every tap

  • Synchronous script in the head

  • Heavy menu JavaScript on click

  • Analytics tags firing complex code after each interaction

Common mistakes

  • Recommending “remove all JavaScript.” Be specific.
  • Ignoring Tag Manager. Old tags pile up for years.
  • Testing only on fast desktops.
1. What does defer do?
2. Long main-thread tasks mostly hurt...
3. A booking plugin loads on every page but is used on one. Fix?

Your action

Next, you will check mobile usability and responsive rendering.

Key terms

Render-blocking resource
A CSS or JavaScript file the browser must download and process before showing the page.
Main thread
The browser thread that runs JavaScript, layout, and painting. When it is busy, the page cannot respond.
Long task
Any main-thread task over 50 milliseconds, a common cause of poor INP.
Third-party script
Code loaded from another company, such as chat widgets, analytics, ad tags, and social embeds.

Questions beginners ask

What does defer do?

It downloads a script without blocking rendering and runs it after the HTML is parsed. Most non-critical scripts should use defer.

What is critical CSS?

The small set of styles needed for above-the-fold content, inlined in the head so the page renders before the full stylesheet loads.

How do I measure a third-party script's cost?

Lighthouse lists third-party usage and blocking time. You can also block a domain in Chrome DevTools and compare results.

Can SEO plugins fix this?

Performance plugins help with minification and deferring, but page builder bloat and heavy widgets usually need template or tool changes.

Related lessons

Want someone to handle SEO for your business while you learn? The team at Remar Digital can help.