Google Search Console is the foundation. It shows real indexing issues, Core Web Vitals, mobile usability problems, and security flags directly from Google's index. Every audit should start here because it's the only tool pulling data from the actual search engine you're trying to rank in. Screaming Frog's free version crawls up to 500 URLs, which covers most small business sites. It finds broken links, redirect chains, duplicate titles, missing meta descriptions, and orphaned pages. For larger sites, you'll hit the limit fast, but it's still useful for spot-checking sections or staging environments. Ahrefs Webmaster Tools is free if you verify your domain. It gives you a site audit score, backlink profile, top pages, and keyword rankings. The crawl depth isn't as granular as paid Ahrefs, but you get enough data to identify major technical debt and content gaps. We use this for clients who need backlink monitoring without paying for a full subscription. SEMrush offers 10 free requests per day through their Project tool. That's enough for a monthly check-in on a single domain. You get crawl errors, HTTPS issues, and basic on-page recommendations. The limit is tight, but it's a decent backup when other tools miss something. PageSpeed Insights and Lighthouse test performance and Core Web Vitals. They're technically not audit tools, but slow sites don't rank, so we run these on every homepage and key landing page. Canadian hosting and CDN choices matter here—servers in Toronto or Montreal add 40–80ms latency for Ottawa users compared to US-based hosts. Most free tools cap features to upsell the paid version. A real audit usually means running Search Console for index health, Screaming Frog for technical crawl, Ahrefs Webmaster Tools for backlinks, and PageSpeed for performance. None of them alone give you the full picture. At Ottawa SEO, we layer all four for new client diagnostics before deciding whether a paid platform is worth it for ongoing monitoring.