Conducting a technical SEO audit on a large-scale website with over a million URLs can seem daunting, but breaking it down into systematic steps can make the process manageable and effective. Here is a detailed approach to follow:
Define the Scope and Objectives:
Clearly outline the objectives of the audit. Are you focusing on improving crawl efficiency, on-page optimization, or resolving indexing issues? Set clear KPIs to measure the success of the audit.
Use the Right Tools:
Employ robust tools capable of handling large datasets such as Screaming Frog, DeepCrawl, OnCrawl, or Botify. These tools are built to manage large websites and provide comprehensive insights.
Crawling the Website:
Begin with a full crawl to understand the existing issues. Depending on the scale, this may take time, so prioritize areas if initial speed is essential.
Analyze Crawl Results:
Look for errors such as 404s, server errors (5xx), and broken links. It’s crucial to resolve these issues to improve user experience and crawl efficiency.
Check for redirect chains or loops.
Review Indexing:
Use Google Search Console to analyze indexing. Ensure that only relevant and quality pages are indexed by checking for duplicate content or unnecessary thin pages.
Implement canonical tags where appropriate and assess the robots.txt file for correct directives.
Page Speed and Performance:
Analyze page speed issues using Google PageSpeed Insights and Lighthouse. Site speed is critical for user experience and search engine rankings.
Mobile-Friendliness:
Ensure the site is fully responsive. Use Google’s Mobile-Friendly Test to identify areas that require improvement for a better mobile experience.
Structured Data and Schema Markup:
Implement and verify structured data. Use Google’s Rich Result Test to ensure it enhances search visualization.
Internal Linking and Structure:
Assess the website’s internal link structure. Ensure a logical hierarchy and the correct distribution of internal link juice to important pages.
Address orphan pages that aren’t linked to elsewhere on the site.
Security:
Ensure the site is secure with an up-to-date SSL certificate, resolving any security vulnerabilities.
XML Sitemaps:
Verify that your XML sitemap is clean, up-to-date, and submitted to search engines properly.
Monitor Logs:
Analyze server log files to understand how search engines are crawling your site. This can highlight crawling inefficiencies and ensure the most crucial pages are prioritized.
Evaluate Pagination:
For sites this large, pagination issues can arise. Ensure that pagination markup is correctly implemented to maintain page continuity and improve indexation.
Regular Monitoring and Updates:
SEO is an ongoing process, especially for large sites. Implement a schedule for regular audits to catch problems early and stay updated with search engine algorithm changes.

By following these steps, you can systematically audit a large website, identifying and rectifying issues that could impair Search Engine Optimization. This comprehensive approach will help improve crawl efficiency, enhance user experience, and ultimately, boost search rankings and traffic.