Devel

Last updated January 2, 2018

Devel is a popular developer module containing a variety of developer and debugging utilities that make it more efficient to perform common development tasks. The Devel module includes the Webprofiler, Devel generate and Kint modules. Devel also features Drush integration and provides several custom Drush commands. Devel and its associated submodules are meant to be used on local development environments and should not be enabled on live production sites.

As a Devel submodule, Webprofiler can give you insight into a variety of performance-related metrics related to database queries and requests and it can also tell you which route and controller are behind any page on your site.
Devel generate is used for generating sample or dummy content like menu items, taxonomy terms, and nodes. The process of using Devel generate to generate content is essentially the same for Drupal 7 and 8.
Kint is a variable debugging tool and provides the kint() function, which is a "pretty-print" version of PHP's var_dump() function.
The main Devel module also provides the debugging function dpm() which can be used to print out debugging messages in the messages block of a page.

Example tasks

Use Webprofiler to learn the names of the routes or controllers responsible for output on any page
Quickly generate dummy content (menu items, terms, and nodes) for a development site
Use Kint to debug a variable during theme development

Confidence

Devel has been a popular developer module and suite of tools since Drupal 6. As such, learning materials exist for Devel that can be quite dated. In addition, the Drupal 8 version of Devel is still in development (although an RC (release candidate) version does exist) and certain utilities or functions may change. While some utilities (such as Devel generate) operate essentially the same way in Drupal 7 and 8, there are many differences between the Drupal 7 and 8 versions.

Drupalize.Me resources

Inspect Variables Available in a Template

Theming, Drupal 8

More information

Knowing how to inspect the variables available within a template file enables you to discover all of the dynamic content in a Twig file, not just that which is already being used.

In this tutorial, we'll learn how to use {{ dump() }}, kint(), vardumper(), and XDebug to inspect variables in a template file.

Goal

Discover and inspect variables available in any template file.

HDCC

Install Webprofiler and Identify Controllers

4m25s // Module Development, Drupal 8

HDCC

Hands-On: Generating Sample Content

3m43s // Site Building, Drupal 7

External resources

Devel (drupal.org)
- The project page for Devel, which describes the submodules and utilities contained within the project.
Drupal 8 Module of the Week: Devel (dev.acquia.com)
- In this interview, project maintainer Moshe Weitzman describes the main modules inside Devel and how they can be used.