The main tools of a back-end web developer are:

1. Server-side programming languages: Back-end developers use programming languages such as Python, Ruby, PHP, Java, or Node.js to write server-side code.
2. Databases: Back-end developers use databases such as MySQL, MongoDB, or PostgreSQL to store and retrieve data.
3. Web Application Frameworks: Back-end developers use web application frameworks such as Django, Ruby on Rails, Laravel, or Express to simplify the development process and provide a structure for the application.
4. API Development Tools: Back-end developers use tools such as Swagger, Postman, or Insomnia to build, test, and document APIs.
5. Deployment and Server Management Tools: Back-end developers use tools such as Heroku, AWS, or DigitalOcean to deploy and manage web applications on servers.
6. Version Control System: Back-end developers use version control systems such as Git to manage code changes and collaborate with other developers.
7. Testing Tools: Back-end developers use testing tools such as JUnit, RSpec, or Mocha to test the code and ensure that it works as expected.
8. Server Monitoring Tools: Back-end developers use tools such as New Relic, Datadog, or Loggly to monitor the performance and logs of servers and applications.

These tools help back-end web developers to quickly and efficiently build, test, and maintain high-quality web applications. The exact tools used will depend on the individual developer’s preferences and the requirements of the project.