Google Search Console and Google Analytics 4 are the foundation—Search Console shows you exactly what Google sees, including indexing errors, Core Web Vitals, and which queries drive clicks. GA4 tracks user behavior and conversion paths. Both are completely free and irreplaceable for serious SEO work. For technical audits, Screaming Frog's desktop crawler is free for up to 500 URLs per crawl, which covers most small to mid-sized sites. It reveals broken links, duplicate titles, missing meta descriptions, and redirect chains faster than any manual check. We use the paid version at Ottawa SEO for larger portfolios, but the free tier handles single-site diagnostics. Keyword research tools worth using: - Ubersuggest gives 3 free searches per day with volume estimates and keyword difficulty scores - AnswerThePublic visualizes question-based queries people actually type - Google Keyword Planner is free with an Google Ads account and shows search volume ranges directly from Google - Google Trends compares keyword popularity over time and by region, useful for seasonal content Ahrefs and SEMrush offer limited free versions—Ahrefs Webmaster Tools requires site verification but provides backlink data and site audits, while SEMrush allows 10 requests per day. Both are useful for competitive gap analysis when you need quick checks without a subscription. PageSpeed Insights and Google's Mobile-Friendly Test are essential for Core Web Vitals monitoring. Bing Webmaster Tools duplicates some Search Console functionality but also offers unique keyword research data and often flags issues Google misses. The catch with free tools is volume limits and restricted historical data. If you're managing multiple clients or a 500+ domain portfolio like ours, you'll hit walls fast. For a single business site or small agency starting out, though, you can run effective SEO for months using only free tools—we did exactly that in 2014 before scaling into paid platforms. The discipline of working within constraints often produces sharper strategy than unlimited data access.