What is HTML?

HTML: definition and significance

HTML describes the structure of a web page: what is a heading, what is a paragraph, a list, an image, a link or a form? To do this, content is marked up with so-called tags, such as the “h1” element for the main heading. Appearance (CSS) and behavior (JavaScript) are separate layers that build on HTML.

HTML was developed in the early 1990s at CERN to connect documents through links. Today, the developer community WHATWG continuously maintains the “HTML Living Standard.” “HTML5” is considered a milestone because, among other things, it introduced video, new form fields and semantic elements.

How an HTML document is built

An HTML document consists of a head section with invisible information such as the page title, meta description and character set, and a body section with the visible content. The browser reads the code, builds a tree structure (the DOM) from it and displays it. Search engines and screen readers evaluate the same structure.

• header, nav, main and footer divide the page into areas
• h1 to h6 form the heading hierarchy
• a sets links to other pages or sections
• img with alt text describes images for screen readers and search engines
• form, label and input build forms with clearly labeled fields

Real-world example: clean HTML instead of “div soup”

A trades business built its website with a website builder. In the source code, almost everything sits in generic containers, headings are just larger formatted text, and images have no descriptions. To visitors the page looks good, but screen readers and search engines cannot recognize any structure.

During the relaunch, the same content is marked up semantically: one H1 per page, logically nested subheadings, labeled form fields, alt texts. Visually, hardly anything changes, but the page becomes easier to find, faster to process and usable for people with disabilities who work with a keyboard or screen reader.

Benefits, common mistakes and imple­menta­tion

Clean, semantic HTML is the foundation for accessibility—the German Accessibility Strengthening Act (BFSG) has applied since June 28, 2025, to certain digital offerings such as online stores for consumers—and for good search engine optimization. It loads faster, is easier to maintain and still works when scripts or styles fail to load. Validation tools such as the W3C validator catch structural errors early.

Nano Concepts builds websites with semantic, valid HTML and checks it against accessibility and technical SEO requirements. This applies to hand-written pages as well as to templates in WordPress or Shopware, where we deliberately improve the automatically generated code instead of adopting it unchanged.

• Choosing headings by font size instead of meaning
• Embedding images without alt text or using images of text
• Building clickable elements without a real link or button
• Creating form fields without an associated label
• Leaving out the language declaration in the document