What Dev Mode Does

Enabling devMode #

devMode is enabled with the general config setting of the same name…

use craft\config\GeneralConfig;

return GeneralConfig::create()
    // ... other settings
    ->devMode(true);

…or by setting the CRAFT_DEV_MODE environment variable:

# ... other environment variables
CRAFT_DEV_MODE=true

It is also on by default for new projects.

devMode Features #

With devMode enabled, you have access to extra information and tools that make working on your project (or a plugin) easier:

• PHP errors and exceptions will be reported in the browser window, with a complete stack trace and code previews;
• Template syntax errors will be reported in the browser with a preview of the offending template;

• Craft will log the following items for each request (some support in Craft 3, expanded Craft 4):

  • Query string variables
  • GET query params or POST body data
  • Active cookies
  • Active session variables

• Multi-line log messages are permitted (Craft 4);

• Info-level messages are written to logs, in addition to those of greater severity;
• PHP warnings and notices are logged (as opposed to just PHP errors and exceptions);
• PHP errors that happen during a request that includes an Accept: application/json header are returned (along with a stack trace) as JSON (Craft 4);
• The control panel’s front-end resource files won’t get cached;
• Twig’s dump() function will be enabled;
• Twig’s debug and strict_variables options will be set to true (see Twig’s Environment Options for more info);
• The global devMode variable in Twig templates is set to true;
• Verbose errors are sent when using GraphQL;
• Queue errors are reported more verbosely in the control panel;
• The Yii debug toolbar can be forced on for the request by sending the X-Debug: enable header;

To reduce the chance of accidentally leaving devMode enabled, each page of the control panel gets a “caution tape” indicator at the bottom of the left sidebar: