Google Search Console is mandatory. It shows you indexing errors, Core Web Vitals, manual actions, and which queries drive impressions. Bing Webmaster Tools gives similar data plus free keyword research and backlink reports that Search Console hides. Both are zero-cost and directly from the search engines. Screaming Frog SEO Spider is free for up to 500 URLs per crawl. That covers most small-to-mid sites and lets you find broken links, duplicate titles, missing H1s, redirect chains, and page speed basics. For larger sites you hit the paywall, but 500 URLs is enough to audit structure and catch glaring technical issues. Google PageSpeed Insights and the Mobile-Friendly Test are single-page tools but useful for diagnosing Core Web Vitals and responsive design problems. PageSpeed Insights pulls real Chrome UX Report data, so you see actual user metrics, not just lab tests. Run your key landing pages through both before you touch anything else. Other free options include Ubersuggest's limited daily scans, Moz's free domain analysis (one query per day), and SEO Minion browser extension for on-page checks and broken-link scanning. Ahrefs Webmaster Tools is free if you verify your site—it gives you a crawl report, backlink data, and keyword rankings, which is generous compared to their paid product. At Ottawa SEO we layer these tools. Search Console and Bing Webmaster run continuously. Screaming Frog gets deployed when we onboard a new domain or troubleshoot indexing drops. PageSpeed Insights goes into every technical audit, especially since Core Web Vitals became a ranking factor in 2021. The constraint with free tools is scale and historical data—you won't get six months of backlink history or rank tracking without paying—but for a one-time audit or ongoing maintenance on a portfolio under 500 pages, the free stack is completely viable. Just don't expect automation or white-label reporting.