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Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
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<?xml version="1.0"?>
<api>
  <help>
    <module>* meta=siteinfo (si) *
  Return general information about the site

This module requires read rights
Parameters:
  siprop              - Which sysinfo properties to get:
                         general               - Overall system information
                         namespaces            - List of registered namespaces and their canonical names
                         namespacealiases      - List of registered namespace aliases
                         specialpagealiases    - List of special page aliases
                         magicwords            - List of magic words and their aliases
                         statistics            - Returns site statistics
                         interwikimap          - Returns interwiki map (optionally filtered, (optionally localised by using siinlanguagecode))
                         dbrepllag             - Returns database server with the highest replication lag
                         usergroups            - Returns user groups and the associated permissions
                         extensions            - Returns extensions installed on the wiki
                         fileextensions        - Returns list of file extensions allowed to be uploaded
                         rightsinfo            - Returns wiki rights (license) information if available
                         languages             - Returns a list of languages MediaWiki supports (optionally localised by using siinlanguagecode)
                         skins                 - Returns a list of all enabled skins
                         extensiontags         - Returns a list of parser extension tags
                         functionhooks         - Returns a list of parser function hooks
                         showhooks             - Returns a list of all subscribed hooks (contents of $wgHooks)
                         variables             - Returns a list of variable IDs
                        Values (separate with '|'): general, namespaces, namespacealiases, specialpagealiases, magicwords, interwikimap, dbrepllag,
                            statistics, usergroups, extensions, fileextensions, rightsinfo, languages, skins, extensiontags,
                            functionhooks, showhooks, variables
                        Default: general
  sifilteriw          - Return only local or only nonlocal entries of the interwiki map
                        One value: local, !local
  sishowalldb         - List all database servers, not just the one lagging the most
  sinumberingroup     - Lists the number of users in user groups
  siinlanguagecode    - Language code for localised language names (best effort, use CLDR extension)
Examples:
  api.php?action=query&meta=siteinfo&siprop=general|namespaces|namespacealiases|statistics
  api.php?action=query&meta=siteinfo&siprop=interwikimap&sifilteriw=local
  api.php?action=query&meta=siteinfo&siprop=dbrepllag&sishowalldb=
Help page:
  https://www.mediawiki.org/wiki/API:Meta#siteinfo_.2F_si
</module>
  </help>
</api>