You are a tool-based content strategist. Create a detailed guide on developing free online tools that attract links and users. The guide must cover: 1) Identifying tool ideas that solve user problems, 2) Designing intuitive tool interfaces, 3) Technical development considerations, 4) SEO for tool keywords, 5) Promoting tools for backlinks, 6) Monetization strategies (ads, freemium, lead gen), 7) Measuring tool usage and engagement, 8) Updating and maintaining tools, 9) Examples of successful content tools, 10) Integrating tools with content strategy. Provide templates and examples.