news://, nntp://, worldwind://, telnet://, svn://, git://, mms:// and mailto: will create a link and an icon but require an agent registered in the browser.
URLs containing certain characters will display and link incorrectly unless those characters are percent-encoded. For example, a space must be replaced by %20 (this can be done using the PATH option of the {{urlencode:}} parser function).
Single apostrophes do not need to be encoded; but unencoded multiples will be parsed as italic or bold markup
Titles containing certain characters will display and link incorrectly unless those characters are encoded with HTML character references.
Even though PHP's urlencode() automatically percent-encodes them, these characters do not get URL-encoded by wfUrlencode(). The ":" symbol is a partial exception – it is not encoded anywhere except for IIS 7.0.
Other URLs associated with a page are constructed by adding a query string. The string can be added to either of the above forms (as in https://en.wikipedia.org/wiki/Train?action=history ), but in this case the system defaults to the second form, i.e. it extends the index.php query string "title=Page_name".
To go to the edit page (or view the source of a protected page): https://en.wikipedia.org/w/index.php?title=Train&action=edit. Other parameters can be added, such as section=5 or section=new to edit or add a page section. There are also parameters for preloading text into the edit box of a new page, as used by the inputbox extension (see mw:Extension:InputBox).
To link to a particular version of a page: https://en.wikipedia.org/w/index.php?title=Train&oldid=1374279 (where oldid is the revision number), or use Template:Oldid. A permanent link to the present version of the page can be accessed by clicking "Permanent link" under "tools" on the left side of the page. The version ID is unique across all pages; the title parameter here has no effect, and can be omitted. Special:PermanentLink/1374279 is a wikilink to a page version.
To link to a diff between two versions of a page: https://en.wikipedia.org/w/index.php?title=Train&diff=1374279&oldid=1260056, where diff is the ID of the version to appear on the right. Set diff=0 to compare the current version; set diff=0 and oldid=0 to compare the two most recent versions. Again the title parameter has no real effect (you can in fact compare versions of two different pages). Special:Diff/1374279 is a wikilink to a diff (documentation).
To perform certain other defined actions, replacing purge in the above example with view, delete, revert, unprotect, info, markpatrolled, validate, render (most of these are available only to administrators).
The below withgadget will work only with gadgets that have been specifically enabled for inline loading. Registered users can load pages at Special:Gadgets by enabling the corresponding gadget at Special:Preferences#mw-prefsection-gadgets.
If constructing URLs for Wikipedia pages, remember to convert spaces into underscores, and to percent-code special characters where necessary, as described in the previous section. (For how to do this in template code, see Templates and programming below.)
Various kinds of error message may appear if an invalid URL, or one to which you do not have access, is submitted. In other cases the URL may redirect to a valid one (for example, page titles are converted to their canonical form as they are when they appear in wikilinks).
enwp.org is not controlled by the Wikimedia Foundation, so it could stop working or change purpose at any time.
The second form can make a long page name into a short code. It uses pageid, which remains accurate even if the page is moved. Pageid has up to 8 digits, shown by clicking "Page information" under "Tools" on the left side of the page.
Note that https://www.wikipedia.org leads to an international Wikipedia portal page, but other URLs beginning with that prefix redirect to English Wikipedia.
Other projects may also use different strings in place of "/w/" and "/wiki/" in URLs. For details, see the URL help page on Meta.
Templates and programming
For use in templates, correct URLs can be constructed using certain magic words and parser functions such as fullurl, urlencode and others. Details of these can be found at mw:Help:Magic words.
Most programmatic interaction with Wikipedia can be performed most efficiently using the API, for which URLs beginning https://en.wikipedia.org/w/api.php are used. For details, see mw:API.