Template

A template is a reusable piece of wikitext that can be transcluded onto other pages. Templates help standardize formatting, centralize maintenance, and provide consistent messages, infoboxes, navigational boxes, citations, and more.

Template namespace

Templates live in the Template: namespace (e.g., Template:Example).
Documentation commonly resides at Template:Name/doc.
Sandboxes and test cases can be kept at Template:Name/sandbox and Template:Name/testcases.

Basic usage

Transclusion:

{{Template name}}

With parameters:

{{Template name|param1=value|param2=value}}

Named parameters improve clarity, especially when many are present.

Parameters

Positional: Template:Name — accessed as {{{1}}}, {{{2}}}.
Named: Template:Name — accessed as {{{title}}}, {{{date}}}.
Defaults:

{{{title|Untitled}}}

 Uses Untitled when title is not provided.

Fallback chains:

{{{author|{{{creator|Unknown}}}}}}

 Tries author, then creator, else Unknown.

Parser functions

Common parser functions used in templates:

Conditional:

{{#if:{{{x|}}}|X provided|X missing}}

Equality:

{{#ifeq:{{{mode|}}}|compact|Compact view|Full view}}

Switch:

{{#switch:{{{type|}}}|A=Alpha|B=Beta|#default=Other}}

Variables (local to page render):

{{#vardefine:FOO|bar}}{{#var:FOO}}

Substitutions:

{{subst:CURRENTYEAR}}

 Renders the current year as a fixed value at save time.

Lua modules

Complex logic can be implemented in Lua under the Module: namespace.
Invoke:

{{#invoke:ModuleName|functionName|arg1=value|arg2=value}}

Use Lua for tasks like string normalization, data lookups, date handling, and performance-sensitive branching.
Keep module code documented at Module:Name/doc where applicable.

Documentation

Place usage instructions on Template:Name/doc and transclude with



Documentation[create] [purge]

.

Include:

 * Purpose and scope
 * Parameters with defaults and types
 * Examples and edge cases
 * Categories for maintenance and discovery

Provide a sandbox and testcases page for safe experimentation.

Sandboxing and testing

Sandbox: editable draft area for changes without affecting live usage.
Testcases: a page with inputs and expected outputs to verify behavior.
Good practice:

 * Test typical and edge inputs
 * Verify categories and template messages
 * Check rendering across skins/devices

Categories and tracking

Add categories directly in templates when needed:

[[Category:Maintenance templates]]

Avoid placing mainspace article categories in templates that will transclude into articles unless appropriate.
Use tracking categories for maintenance:

{{#if:{{{date|}}}||[[Category:Pages missing dates]]}}

Hide categories in documentation using ... when relevant.

Noinclude, includeonly, onlyinclude

... — content only on the template page (not transcluded).
— content only when the template is transcluded.
... — only the marked part is transcluded (rest ignored).
Typical pattern:

  <includeonly>Banner content</includeonly><noinclude>{{Documentation}}</noinclude>

Substitution

{{subst:Template name}} writes the template’s wikitext into the page at save time.
Useful for signatures, one-time notices, or when the resulting text should not update with future template changes.

Common mistakes

Unbalanced tags: missing {{ or braces causing parse errors.
Placing categories that leak into articles unintentionally.
Overusing complex logic without documentation, making maintenance difficult.
Missing defaults causing empty labels or layout breaks.
Not escaping pipe characters | within table cells or links when needed.

Escaping and formatting

Pipes in links or tables can be escaped with {{!}} if the site provides a helper.
Code and examples can be wrapped in ... to preserve formatting.
For table templates, ensure consistent cell separators and header styles.

Performance considerations

Minimize deeply nested conditionals; prefer Lua for heavy logic.
Reuse shared modules for repeated computations.
Avoid excessive #invoke calls per render if a single call can batch the work.

Design guidelines

Make parameters explicit and self-documenting.
Provide sensible defaults to avoid blank outputs.
Keep styling consistent with site conventions; use minimal inline CSS.
Separate data and presentation where feasible (module returns data; template formats it).

Versioning and deprecation

Mark deprecated parameters in documentation and maintain backwards compatibility where possible.
Consider a compatibility wrapper template to redirect old usage to new logic.

Examples

Simple message:

<includeonly><div class="notice">Hello {{#if:{{{name|}}}|{{{name}}}|there}}!</div></includeonly><noinclude>{{Documentation}}</noinclude>
Usage: {{Example|name=World}} → Hello World!

With categories and documentation:

<includeonly>
<div class="box">This page needs citations.</div>
[[Category:Maintenance messages]]
</includeonly><noinclude>
{{Documentation}}
</noinclude>

Lua-backed:

-- Module:Greeter
local p = {}
function p.greet(frame)

 local name = frame.args.name or "there"
 return "Hello " .. name .. "!"

end
return p

<includeonly>{{#invoke:Greeter|greet|name={{{name|}}}}}</includeonly><noinclude>{{Documentation}}</noinclude>

Help:Template