What is HTML?

What is HTML?

HTML (HyperText Markup Language) is the standard markup language for creating web pages and web applications. Created by Tim Berners-Lee at CERN in 1991, HTML defines the structure and content of a web page using a system of tags and attributes enclosed in angle brackets. Every web page you visit is built on an HTML document that your browser interprets and renders as a visual page.

HTML documents are plain text files with the .html or .htm extension. They contain elements like headings, paragraphs, links, images, tables, forms, and embedded media, defined by start and end tags. Modern HTML5 (standardized in 2014) added native support for audio, video, canvas drawing, semantic structural elements, and offline capabilities. HTML works together with CSS for styling and JavaScript for interactivity to form the three foundational technologies of the web.

How HTML Works

HTML stands for HyperText Markup Language, and it is the language that describes the structure and meaning of a web page rather than its exact appearance. An HTML document is plain text marked up with tags written in angle brackets, such as <p> for a paragraph or <h1> for a top-level heading. Most tags come in pairs that wrap content, an opening tag and a matching closing tag like </p>, and the content between them is what the tag describes.

When a browser loads a page, it parses the HTML into a tree of nested objects called the Document Object Model, or DOM. Each element becomes a node, and the nesting of tags in the source becomes the parent-child structure of the tree. This tree is what the browser actually renders and what scripts read and modify, so the same markup produces a live, structured document rather than a static image of a page.

HTML deliberately handles only structure. Presentation is the job of CSS, which selects elements and applies colors, spacing, fonts, and layout, and behavior is the job of JavaScript, which manipulates the DOM in response to events. This separation of concerns, structure in HTML, style in CSS, behavior in JavaScript, is the foundation of how modern web pages are built. Certain elements also carry semantic meaning, like <nav>, <article>, and <header>, which help browsers, search engines, and assistive technologies understand a page's parts.

A key property is fault tolerance. Browsers are built to render HTML even when it is imperfect, filling in missing tags and recovering from small errors rather than refusing to display the page. This forgiving behavior is a large part of why the web scaled so quickly, though it also means two browsers can occasionally interpret sloppy markup differently.

History and Standardization

HTML was invented by Tim Berners-Lee at CERN around 1990 and 1991 as part of his creation of the World Wide Web. The first version was a small set of tags for linking and structuring documents, and its defining idea was the hyperlink: the ability to reference and jump to any other document, which is what turned a collection of files into a web.

Standardization moved to the World Wide Web Consortium (W3C), which published the widely used HTML 4 specification in the late 1990s. An attempt to reformulate the language as strict XML, called XHTML, followed but never fully displaced ordinary HTML. The pivotal modern step was HTML5, developed largely by the WHATWG and later aligned with the W3C, which added native audio and video, canvas graphics, and many semantic elements.

Today HTML is maintained by the WHATWG as a continuously updated Living Standard rather than a series of numbered versions, so the language evolves in place as browsers implement new features. It is one of the three core open technologies of the web alongside CSS and JavaScript, and it remains completely free and royalty-free, which is central to the web's openness.

HTML Compared to Other Document Formats

Against a fixed format like PDF, the contrast is reflow versus fixed layout. HTML is fluid: the same document adapts to any screen size, from a phone to a wide monitor, because the browser lays it out at display time. A PDF, by design, preserves an exact fixed page. HTML is therefore the natural choice for content meant to be read on any device and updated freely, while PDF wins when the precise printed appearance must never change.

Against a word-processor format like DOCX, HTML is open, text-based, and universally readable without special software, since any browser can open it. DOCX is optimized for authoring and editing rich documents with tracked changes and precise print layout. HTML is not primarily an editing format; it is a delivery and structure format, which is why authors often write in something else and publish to HTML.

Compared to a lightweight markup language like Markdown, HTML is more verbose and more powerful. Markdown is easy for humans to write by hand but is limited in what it can express, and in practice it is almost always converted into HTML for display. HTML sits at the center of the web precisely because it is the common target that other formats compile down to, the structural language every browser understands directly.

Technical Details

HTML vs Other Document Formats

HTML powers reflowable web content, while PDF preserves fixed page layout for distribution.

Pros and Cons

When to Use HTML

Here are the most common situations where HTML is the right choice: