ParserfunctionsEdit
Parserfunctions are a set of conditional rendering tools built into the MediaWiki platform through the ParserFunctions extension. They empower editors to write templates that respond to page state, input parameters, and user context, rather than duplicating content across many pages. In large wikis, where consistency and maintainability are crucial, parserfunctions help keep content accurate and up to date with far less manual labor. They are a practical mechanism for ensuring that readers see the right information in the right context without forcing editors to repeat themselves across dozens of pages. The extension is part of the broader ecosystem around MediaWiki and the way templates can be used to present information consistently across a wiki.
Overview
Core capabilities
Conditional rendering through #if, allowing a template to return one string when a condition is true and another when it is false. This makes templates adaptable to different pages or user contexts.
Equality tests with #ifeq, which compare two values and return content accordingly. This is useful for presenting alternate wording or formatting when a parameter matches a particular string.
Multi-way branching via #switch, which matches a value against a list of cases and renders the corresponding content. This is efficient for templates that need to cover several discrete outcomes without a long chain of nested conditions.
Arithmetic and expression evaluation with #expr, enabling templates to compute values or format content based on numeric or string expressions.
Existence checks with #ifexist, which lets editors tailor output based on whether a particular page exists, a template is present, or a category contains items. This is especially helpful when presenting links or notices that depend on content availability.
Typical usage patterns
Page-aware messages: a template can display a warning or a note only on certain pages, avoiding clutter on pages where it isn’t relevant.
Language and date formatting: templates can switch wording or date formats depending on user language or page region, improving readability without duplicating content.
Dynamic navigation: a single template can present different navigation links depending on page state or user permissions, reducing maintenance overhead for site-wide navigation changes.
Existence-based prompts: if a page exists, a link can point there; if not, a suggestion for creating the page can be shown instead.
Practical examples
Display a message only on the main page: {{#if:{{PAGENAME}}|Main page is active for navigation|You are viewing a non-main page}}. This leverages the #if function to tailor content to the current page name.
Show different wording based on a page name match: {{#ifeq:{{PAGENAME}}|Main Page|This is the primary entry point|This is a secondary entry point}}. This uses #ifeq to compare values and render accordingly.
Offer multiple outcomes with a switch: {{#switch:{{PAGENAME}}|Home=Home page|About=About page|Other=Other content}}. This demonstrates how #switch streamlines several branches.
Compute a value: {{#expr: 3 + 5 * 2}}. The #expr function evaluates arithmetic expressions and can be used inside templates wherever a calculated value is needed.
Check for existence of a page: {{#ifexist:SomePage|That page exists|That page does not exist}}. This enables content that reacts to content availability.
For more background on the kinds of tokens involved, see the general documentation for the extension and related Template practices in MediaWiki environments.
Features and design considerations
Consistency and maintenance
Parserfunctions help prevent duplication by letting templates adapt content to context. This supports a principle often valued in more performance-conscious environments: fewer moving parts means fewer opportunities for drift between pages. By centralizing logic in templates, editors can update behavior in one place and have it reflected across many pages. See also Template design patterns and how conditional content is implemented at scale.
Performance implications
While parserfunctions are powerful, overuse or deeply nested logic can impact template rendering time, especially on very large wikis with heavy template usage. Proponents argue that the payoff in reliability and consistency typically outweighs the cost, but practitioners should balance functionality with maintainability and load patterns. See discussions around Software design and performance in template-heavy systems.
Security and reliability
Expression evaluation and page-existence checks rely on server-side logic, which means editors should be mindful of potential edge cases or malformed inputs. When used responsibly, parserfunctions contribute to a predictable rendering pipeline and reduce the risk of dangling or inconsistent content across pages.
Debates and practical viewpoints
Some editors worry that excessive templating can obscure content and hinder new contributors who must learn a layer of logic to edit effectively. Supporters respond that well-documented templates and sensible usage guidelines keep the learning curve manageable while delivering durable, scalable content structures. Critics may point to maintenance debt generated by long chains of conditions, but advocates emphasize disciplined template design and versioned documentation as best practices.
Implementation and ecosystem context
Parserfunctions are part of the broader approach to extending the capabilities of MediaWiki through extensions. They interact with the parser used by the software to render pages, enabling dynamic behavior in templates and transclusions. The features described here are widely adopted across large wikis and are commonly discussed in the context of template authorship, Template best practices, and the ongoing evolution of the wiki engine.