Following Wikipedia:Protection policy, page protection may be permanently applied to all templates which have been identified by the community as being of high risk to Wikipedia. If fully protected, so that they can only be edited by administrators, these templates should be changed only after consensus for the change has been established on the template's talk page. If semiprotected, templates may be edited by any established user, but users should ensure there is consensus for their edits and avoid edit wars on templates.
The most common reasons a template is considered high-risk are:
- The template is used in a highly visible location, such as the main page.
- The template is transcluded into a very large number of pages.
- The template is substituted extremely frequently on an ongoing basis (for example, templates used to warn users about inappropriate editing).
There are no fixed criteria, and no fixed number of transclusions, that are used to decide whether a template is high-risk. Each template is considered separately.
There are two reasons high-risk templates are protected: vandalism and server load.
Vandalism — The risk of vandalism to a template transcluded thousands of times is obvious. Although this kind of vandalism is reverted very quickly (often within one minute), it might be seen by thousands of viewers before it is removed. Protection of highly-used templates lowers this risk.
Server load — Whenever a template is edited, the wiki software not only updates the template, but every page that transcludes the template. For example, if template A is transcluded in 1000 articles, then editing A effectively changes all 1000 articles (plus the template). The Mediawiki software has been written to make it impossible to mount a denial-of-service attack in this manner.
Instead of being recompiled instantly, the pages that need to be recompiled are listed in the job queue and are slowly recompiled as other edits are made, spreading out the load. It would be possible to make the job queue extremely large by repeatedly editing a particular highly-used template. This would present only an inconvenience, however, and would not bring down the site.
A side effect of the job queue is that it can take some time for changes to a template to become visible in all pages where the template is used. This can cause confusion among inexperienced users, who believe the template is broken and attempt to fix it instead of waiting for the changes to work through the job queue. Protection of highly-used templates helps to ensure that only editors familiar with the effects of editing templates make the changes.
- Wikipedia talk:Protection policy/Archive 2#Template protection
- Wikipedia:Administrators' noticeboard/IncidentArchive57 #Spurious obscenities
- Wikipedia:List of indefinitely protected pages#High use templates – an incomplete list of templates protected per this guideline.
- Wikipedia:Template documentation#How_to_create_a_documentation_subpage – A method to securely split template documentation off from template code in a separate page. Enables full protection of template code while retaining the documentation part unprotected, so that everyone can still edit the documentation.