The Devel Module provides several tools that are extremely useful for Drupal development, including cache management, SQL debugging tools, investigation tools, a module reinstaller, an API reference tool, and many more.

You can find out more about this module at the official website: http://drupal.org/project/devel.

The main part of this module (the Devel module) provides these tools as items in a block. So after installing the module, you will need to go to Administer | Site building | Modules and enable the module, and then go to Administer | Site building | Blocks to tell Drupal where to display the new content.

This module also includes tools for building themes, a macro generator to simulate form data entry, and a tool to generate testing data. As the module continues to improve, new features will be added as well.

Any serious module developer will want to install the Devel module. In the writing of this book, it has proven an invaluable tool for reinstalling modules, clearing caches, and debugging difficult code.

As we shall see in this book, Drupal developers adhere to strict conventions in their code. The Coder Module is a tool designed to help you, the developer, locate and fix code that does not adhere to these conventions.

In addition to making sure code follows conventions, it also does some basic security auditing regarding how text is handled. This can be useful for spotting mistakes before they become security risks.

The Coder Module is also hosted on the official Drupal site: http://drupal.org/project/coder.

While it does not improve productivity in the same way that the Devel module does, Coder can help you generate clean and "Drupalish" code. Its strict syntax checking also occasionally turns up bugs.

In addition to these modules, there is a wealth of information on the Drupal website about how to configure your favorite development environment (including Emacs, VI, FireBug, and Eclipse PDT) for Drupal development: http://drupal.org/node/147789.