What Is WordPress?

WordPress started in 2003, when Mike Little and Matt Mullenweg forked b2/cafelog, an earlier blogging tool. Today it runs far more than blogs: company sites, news outlets, online shops built with extensions such as WooCommerce. Its licence, GPLv2 or later, lets anyone run the program for any purpose, study how it works, change it and redistribute it.

Two names are easy to mix up. WordPress.org is the open-source project's site, where you download the software to install on your own hosting. WordPress.com is a commercial service that hosts sites on that same software. With the first, you decide what runs on the server; with the second, the provider makes some of those decisions for you.

Its market share is high, but the figure depends on who is counting. W3Techs, which publishes a daily report with its own documented method, put WordPress at 40.1% of all websites and 58.6% of sites with an identifiable CMS on 8 October 2026. The project's official page says "over 43%" without explaining how it counts. If you need one number, the measurement with a published method is the stronger reference.

A WordPress installation has three layers. The core handles users, content, media and the database. The theme decides how that content is presented. Plugins add features: forms, a shop, caching, SEO. When a visit comes in, WordPress reads the content from the database, combines it with the theme's templates and generates the HTML. A caching plugin or a server-side cache can store that result so the work is not repeated on every visit.

Since version 5.5, the core generates an XML sitemap by default at /wp-sitemap.xml. If the setting that asks search engines not to index the site is switched on, that sitemap is disabled. Many SEO plugins replace it with their own. What the core does not include is a field for the meta description: editing it takes a plugin or custom code.

WordPress also offers a REST API that delivers content as JSON. Through it, another program can read posts and pages and build the website on its own. This is known as headless WordPress: WordPress stays as the editing back end, and a different system generates the public site.

With four in ten websites running on WordPress, according to W3Techs, it pays to know the faults that come from its configuration, because you can look for them in the same places on any WordPress site. Three are classics: the no-indexing setting left on after launch, two sitemaps active at once because the core and a plugin each provide one, and plugins that load their code on every page even though only one page uses them.

For AI search the same applies as for Google. Crawlers read the HTML the server delivers, not what the admin screen shows. If a caching plugin, the theme or a separate front end changes that HTML, the setting in the back end no longer proves what search engines actually see.

This website is an example. zds.es keeps and edits its content in WordPress, but its pages are generated by Astro, which pulls that content through the REST API; the source code of any page names "Astro" as its generator. That is why /wp-sitemap.xml returns a 404 error on zds.es (checked 8 October 2026), and the sitemap listed in robots.txt comes from the front end. On a headless setup, checking the plugin's sitemap tells you nothing about the sitemap Google and AI crawlers read.

• Right after launch, check that the setting asking search engines not to index the site is switched off.
• Keep a single sitemap active, either the core's or the SEO plugin's, and declare only that one in robots.txt and Search Console.
• Keep the core, theme and plugins up to date. According to W3Techs, 35.2% of WordPress sites were not yet on version 7 on 8 October 2026.
• Install only the plugins you use, and check whether two of them do the same job, especially for SEO and caching.
• Check the title, meta description, canonical and structured data in the HTML the browser receives, not in the editor.
• Measure speed with field data after changing the theme or adding plugins, not only with a lab test.

• Moving a staging site to production with the no-indexing setting still on.
• Running two active sitemaps with different URL lists.
• Trusting the SEO configuration because the WordPress back end shows it, without looking at the served HTML. With caching or on a headless setup, the two can differ.
• Installing two SEO plugins at once, which ends up producing duplicate tags.
• Signing up for WordPress.com expecting the same control over the server as with your own installation.