A web browser application is software that retrieves web pages, displays them, and lets you move between them by following links. It is the most familiar kind of web user agent, meaning software that interacts with websites on behalf of its user. Most browsers use a rendering engine to turn a page’s code into the layout you see on screen.
What a web browser application does
MDN Web Docs, Mozilla’s developer reference, describes a web browser as a program that retrieves and displays web pages and lets users reach additional pages through hyperlinks. Three functions define it: fetching content from a server, presenting that content, and navigating between documents. Anything that lacks one of these is not a browser in the ordinary sense.
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MDN also notes that browsers typically rely on a rendering engine. That engine parses the page’s HTML, CSS and scripts and converts them into the visual output. Google Chrome’s Blink, Apple’s WebKit and Mozilla’s Gecko are examples of engines that browsers use, though the engine is an internal component rather than the browser itself.
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Browser versus web user agent
A web user agent is a broader category. The W3C Web User Agents Group Note Draft, dated 23 September 2026, defines it as software that interacts with websites outside itself on behalf of its user. That includes rendering content and carrying out actions the user requests or authorizes. The same draft states that the web browser is the most common type of web user agent.
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The practical difference is scope. Every browser is a user agent, but not every user agent is a browser. Other software can act for a user on the web, such as tools that fetch and act on pages without presenting a navigable interface. The browser is the case most people encounter, which is why the term is often used for the whole category.
Browser-like components inside other apps
The boundary matters most when a browser-like component sits inside a larger program. The W3C draft gives a clear rule of thumb: any product that can load arbitrary content is a web browser. That includes in-app browsers that can follow cross-site links, which means a chat app or email client that opens external websites may be functioning as a browser.
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The W3C draft distinguishes between two kinds of embedded components:
| Component | Acts as a user agent on its own? | Why it matters |
|---|---|---|
| SFSafariViewController (iOS) | Yes, as a library that takes on user-agent duties | It distinguishes external content from the host app’s own content. |
| Android Custom Tabs | Yes, as a library that takes on user-agent duties | It distinguishes external content from the host app’s own content. |
| Generic WebView library | No, not a user agent on its own | The embedding app remains responsible for any user-agent behavior it provides. |
When an app embeds a generic WebView and adds its own browsing controls, the app itself takes on the browser’s responsibilities. Whether the label applies therefore depends on what the component and the embedding application actually do, not on the name a developer gives it.
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Installed web apps are not browsers
A web application is content accessed or run with web technologies. The W3C Web Application Manifest specification explains that a user agent may let a web app be installed and launched with manifest settings applied. Once installed, the app can appear with a home-screen icon and open without browser tabs or an address bar, so it looks like a native app.
That presentation does not make the installed app a browser. The browser is still the user agent that loads and runs the app’s content. The installed app is the content, launched through the browser’s manifest support.
Quick checks for classifying software
- Does it fetch web pages from servers and show them to the user?
- Can the user move to other pages by following links, including links to other sites?
- If it is part of another app, does it open external content with its own user-agent behavior, or only display the host app’s own pages?
- If it is a web app launched from an icon, is the web content running inside a browser engine rather than being the browser itself?
If the first two answers are yes, the software is a web browser application under the MDN definition. The embedded and installed cases require the more careful reading described above.
Scope and status of the guidance
The MDN glossary entry is a concise reference for the browser definition. The W3C Web User Agents document is a Group Note Draft, which the W3C describes as a work in progress and inappropriate to cite as anything else. Its boundary guidance reflects current W3C thinking, not a settled normative rule. The Web Application Manifest specification is the source for installed web app behavior.
Definitions of user agents and browsers may evolve as the W3C finalizes its guidance, so treat the embedded-component classifications as current draft positions.
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