Prepopulate

The Prepopulate module allows fields in most forms to be pre-populated from the $_REQUEST variable.

Prepopulate is excellent for creating bookmarklets. For examples on usage for all of these cases, please read the USAGE file that comes with the module or you can read the online handbook page.

Drupal 8

The format in D8 has changed. It uses the field/form array structure. This typically means you should use [widget][0][value] as part of the URL for field backed form inputs.

Pre-populate the title field on a node creation form:
- http://www.example.com/node/add/page?edit[title][widget][0][value]=simple title

Pre-populate the body field:
- http://www.example.com/node/add/page?edit[body][widget][0][value]=hello world

Pre-populate an entity reference field:
- http://www.example.com/node/add/page?edit[field_entity_reference][widget][0][target_id]=123

Note: For security reasons, Drupal 8 version of this module does not support radios/checkboxes. This means by default, someone cannot craft a specially formatted URL that automatically adds permissions (checkboxes) or changes admin config options (radios). Nor does it support overwriting any existing values in inputs. The later cannot be turned off. But if you really need radios/checkboxes, implement hook_prepopulate_whitelist_alter to add additional allowed form elements. Use with caution.

Drupal 7

In previous version of Drupal, the following URL example will work:

http://www.example.com/node/add/blog?edit[title]=this is the title

It will automatically fill the Title field on a new blog post with the words "this is the title". Any field can be prepopulated this way, including taxonomy and CCK fields. You can prepopulate more than one field at a time as well.

Important Note
As of Prepopulate 7.x-2.1 the ability to base64 encode request parameters has been removed. See this security advisory for more information.