Substitution is a different way of handling templates than normally done on Wikipedia. Usually, templates are transcluded, which means that if the template changes, every page that uses it will update to comply with the change-in-question. This is the procedure used for most templates. However, some templates are instead substituted. This means that if the template changes, the page that uses it will not, and will continue to show the old version of the template. Some templates should always be substituted, while most should always be transcluded.
This page also lists templates that should either always or never be substituted except in the Wikipedia namespace. Automated tools (a.k.a. bots) that do such replacements will never be used on the original template. If you are going to use a bot to substitute templates, please read through the talk page first, as many are under dispute or change status over time, and substitution is permanent.
Ordinarily, a template will be expanded "on the fly"; that is, the template code on a page calls a separate page every time it is rendered. Although most page views are served from the cache, pages need to be rendered for previews and rendered again when the page changes. When someone is editing a page with a normal template call, they see the template call.
Additionally, when creating or editing templates that are commonly substituted, adding a hidden comment to the template page helps article editors to see how templates are being used (e.g.
<!-- Substituted from Template:Documentation -->).
This is a list of templates that should always be substituted, organized by namespace. Each list is ordered alphabetically with grouped series. This is not a comprehensive list; other less-used templates may also need to be substituted, see the template's documentation for details.
These templates have a purpose and/or syntax that require them to be substituted.
This is a list of templates that should not be substituted. This is because they contain formatting standard code, contain complex code, or contain code that breaks if substituted.
These templates, used in the main-space, add a comment about why an article is misnamed. They may be removed as the MediaWiki titling facilities improve, and the wording/layout may change.
See Category:Chemical element symbol templates. These are used to simplify the entry of chemical formulae.
Most templates related to renaming or deleting pages are used temporarily, and thus do not need to be substituted (it just makes more work to delete them).
The following templates must be substituted in order to work correctly: