Google Search Console is non-negotiable. It shows you exactly what Google sees: indexing errors, Core Web Vitals, manual actions, and which queries drive clicks. Pair it with Google Analytics 4 for traffic patterns and user behavior. These two are the foundation of any SEO operation, free or paid. For technical audits, Screaming Frog's desktop crawler is free up to 500 URLs per crawl. That covers most small to mid-sized sites and catches broken links, redirect chains, duplicate titles, and missing meta descriptions faster than manual checks. We run it on new client sites before touching anything else. Ahrefs Webmaster Tools gives you free backlink data and site audits if you verify ownership. It won't match their paid product's depth, but you get Domain Rating, referring domains, and top pages without the $99/month subscription. Ubersuggest offers 3 free searches per day for keyword volume and difficulty, enough for planning a few blog posts or pages. PageSpeed Insights and Lighthouse (built into Chrome DevTools) measure Core Web Vitals and surface performance bottlenecks. Mobile-Friendly Test confirms responsive issues Google would penalize. Both are Google's own tools, so they reflect what actually matters for rankings. Answer the Public visualizes question-based queries around a seed keyword. It's useful for content planning when you need to see what people ask about roofing in Ottawa or accounting in Toronto. The free tier limits daily searches but doesn't paywall the visualization. What these free tools don't do well: deep competitor analysis, historical rank tracking, or large-scale keyword discovery. You'll hit walls around 10,000 backlinks analyzed or 50 keywords tracked. At Ottawa SEO, we use free tools for new projects and clients testing the waters, then move to paid platforms like Ahrefs or Semrush when the domain portfolio or traffic justifies the cost. Free tools are enough to diagnose problems and plan fixes; they're not enough to run a 500-domain operation or compete in saturated verticals.