A proper site audit needs data analysis, code validation, and research, and none of that requires a paid SEO subscription to get started. Plenty of free tools match what their paid counterparts offer for a basic audit. Here’s a working list to start with.
1. SEO Ngram Tool
SEO Ngram Tool analyzes word-combination frequency and patterns (n-grams) in content, useful for spotting keyword trends and repetition patterns across a site.
2. Answer The Public
Answer The Public visualizes the actual questions people search around a keyword, as a web/cloud diagram, useful for finding content gaps rather than just keyword volume.
3. Ahrefs Free Keyword Tool
Ahrefs Free Keyword Tool gives search volume and keyword difficulty for a given term, a scaled-down version of Ahrefs’ paid keyword explorer.
4. Siteliner
Siteliner scans for duplicate content, broken links, and internal linking structure across a whole site, not just single pages.
5. W3C Validator
The W3C Markup Validation Service checks HTML against web standards and flags markup errors that can affect rendering and accessibility.
6. Screaming Frog
Screaming Frog crawls a site and reports on titles, meta descriptions, headings, broken links, and duplicate content, still the closest thing to an industry-standard technical crawler.
7. Netpeak Spider
Netpeak Spider covers similar ground to Screaming Frog, broken links, duplicate content, meta tags, page speed, a reasonable alternative if you want to compare crawlers.
8. Xenu Link Sleuth
Xenu’s Link Sleuth checks for broken links and missing images. Worth flagging honestly: development on Xenu has been dormant for years, it still runs and does the basic job, but don’t expect active updates or support if something breaks.
Mobile SEO
9. MobileMoxie
MobileMoxie focuses specifically on mobile search: a Mobile SERP Test Tool, mobile page-click analysis, and mobile rank tracking.
Technical Audit Tools
10. DNS Propagation Checker
whatsmydns.net shows whether DNS changes have propagated across servers worldwide, useful right after a migration or DNS update.
11. MX Toolbox Blacklist Check
MX Toolbox Blacklist Check checks whether a domain or IP has landed on an email blacklist, relevant if transactional or marketing emails are landing in spam.
Security Audit Tools
12. WPScan
WPScan is a WordPress-specific vulnerability scanner, checks core, plugins, and themes against a known vulnerability database.
13. SSL Labs Security Checker
Qualys’s SSL Labs grades your SSL/TLS certificate configuration and flags weak ciphers or misconfigurations most site owners wouldn’t catch manually.
14. Hacker Target Drupal Security Scanner
The Drupal Security Scanner is the Drupal-specific equivalent of WPScan, relevant if you’re auditing a Drupal site rather than WordPress.
Performance Tools
15. GZip Compression Checker
GZip Compression Checker confirms whether a server is actually compressing responses, a quick win for load time if it isn’t.
16. YSlow
YSlow, originally from Yahoo, audits page speed and gives optimization recommendations. Worth noting: Yahoo no longer actively promotes or develops it, and the ecosystem has largely moved to Lighthouse and PageSpeed Insights for this job, so treat it as a secondary check rather than a primary one.
17. GTmetrix
GTmetrix remains one of the more detailed free performance analyzers, waterfall charts, load time breakdowns, and specific optimization suggestions.
Free Google Tools
- Google Search Console: indexing status, keyword performance, click-through rates, mobile usability, and crawl errors, all from Google’s own data.
- Google PageSpeed Insights: site speed analysis and optimization suggestions, both mobile and desktop.
- Google Analytics: traffic and behavior data that’s genuinely useful for content and structure decisions, not just vanity metrics.
- Google Mobile-Friendly Test: flags whether a page passes Google’s mobile-usability bar.
- Rich Results Test: Google retired the old Structured Data Testing Tool and migrated non-Google-specific validation to the separate Schema Markup Validator. Use Rich Results Test for how Google specifically will render your markup, and Schema Markup Validator for general schema.org compliance.
- Lighthouse: built into Chrome DevTools now rather than a separate extension, audits performance, accessibility, best practices, SEO, and PWA compliance in one pass.
Summary
None of these tools alone replaces a full audit. Realistically, a proper audit means combining a crawler (Screaming Frog or Netpeak Spider) with Google’s own tools (Search Console, PageSpeed Insights, Rich Results Test) plus a security scan if the site handles any sensitive data. Free covers the fundamentals; paid tools mostly add scale and automation on top.