What Dev Mode Does

devMode is intended only for local development. It should never be enabled on a public server, as it can expose parts of your system (and its users) that can otherwise be considered private.

Enabling devMode #

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

use craft\config\GeneralConfig;

return GeneralConfig::create()
    // ... other settings

…or by setting the CRAFT_DEV_MODE environment variable:

# ... other environment variables

It is also on by default for new projects, so that you can use the web-based installer.

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 and later);

  • 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 and later);
  • The Yii debug toolbar can be forced on for the request by sending the X-Debug: enable header;
  • Verbose errors are sent when using GraphQL;
  • Queue errors are reported more verbosely in the control panel;
  • 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;
  • Craft’s graphical setup wizard is enabled;

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:

Craft Control Panel, devMode enabled

Craft control panel with devMode enabled, indicated by the “caution tape” in the lower-left corner.

Applies to Craft CMS 4 and Craft CMS 3.