Mastering Ruby on Rails requires not only a grasp of its core principles but also familiarity with essential tools that can enhance a developer's workflow. Among the most valuable tools are Git for version control, which allows for seamless collaboration and tracking of changes, and RSpec, a powerful testing framework that promotes test-driven development. Additionally, employing Bundler helps manage application dependencies, ensuring that gems are installed and maintained efficiently. Other noteworthy tools include:

1. Rails Admin for easy administration of your application
2. Pry for debugging and examination of code
3. Capistrano for automated deployment

Furthermore, developers should be well-versed in using Docker to create consistent environments across development, testing, and production. This containerization approach provides flexibility and mitigates issues arising from discrepancies between different systems. Moreover, implementing Webpacker facilitates seamless integration of modern JavaScript frameworks with Ruby on Rails applications, enabling smoother user experiences. By mastering these essential tools, developers can sharpen their productivity and enhance their projects, ensuring they stay ahead in the fast-evolving landscape of web development.

Optimizing the performance of your Ruby on Rails application is essential for delivering a seamless user experience. Here are 5 tips to help you cook up a high-performance Ruby on Rails application:

1. Leverage Caching: Utilize Rails built-in caching mechanisms to store frequently accessed data, significantly reducing the load on your database and speeding up page render times.
2. Optimize Database Queries: Ensure your database queries are efficient by using tools like Bullet to identify N+1 query issues and properly indexing your database.
3. Use Background Jobs: Offload heavy processing tasks to background jobs using Sidekiq or Delayed Job to keep your application responsive.
4. Minimize Asset Requests: Use the asset pipeline effectively by compressing CSS and JS files, and consider serving static assets through a Content Delivery Network (CDN).
5. Regularly Review Your Code: Conduct code reviews and refactor any outdated or inefficient code to maintain a clean codebase and improve overall performance.

Building scalable Ruby on Rails projects requires a solid foundation of key ingredients that ensure both performance and maintainability. One of the most critical components is a well-structured architecture, which involves implementing design patterns such as MVC (Model-View-Controller) to promote separation of concerns. Additionally, it's essential to utilize gems that enhance functionality without compromising application speed. Some notable gems include Active Record for database interactions and Sidekiq for background processing, which are vital for handling large amounts of data and user requests efficiently.

Another important ingredient for scalable Ruby on Rails projects is database optimization. This can be achieved by employing indexing strategies that speed up query performance and leveraging caching mechanisms to reduce database load. Furthermore, adopting a microservices architecture can significantly enhance scalability by allowing different parts of the application to be updated independently. Lastly, a robust testing framework is necessary to maintain code quality and ensure that any scalability changes do not introduce new bugs or issues.