"There isn't a single universally agreed answer, because it depends on what you mean by "feature the World Wide Web."

If you mean **the actual World Wide Web created by** Tim Berners-Lee (which became publicly available in 1991), then the earliest known fiction that explicitly incorporates the Web appears to be from **1993–1994**, when the Web was still very new. Literary historians haven't identified one clear "first" work that everyone accepts. ([Wikipedia][1]) by William Gibson envisioned a vast interconnected digital information space and is frequently credited with popularizing concepts that resemble the modern Web and cyberspace. citeturn0search4

* by Vernor Vinge depicted immersive networked virtual worlds and online identities years before the Web. citeturn0search1
* described a globally accessible information network that many readers later compared to the Web. to works such as (1981) or Neuromancer (1984), depending on the criteria used. ([Goodreads][2])

[1]: https://en.wikipedia.org/wiki/WorldWideWeb?utm_source=chatgpt.com "WorldWideWeb"
[2]: https://www.goodreads.com/book/show/25410471-true-names-and-the-opening-of-the-cyberspace-frontier?utm_source=chatgpt.com "True Names and the Opening of the Cyberspace Frontier by Vernor Vinge | Goodreads"

Not convinced this is the thing that's going to cure cancer, guys...

Only 500 www servers by end of 1993. 1994 was big year and home dialup with Mosiac. 10,000+ servers in 1994
Original Win95 was no more Internet ready out of the box than 1993 versions of Win3.x / WFW3.x.

I'm confident fiction will be in a book published in 1995 & maybe started in 1994 on romance or detective theme.
Wire Romance in 19th C.

We had it in 1994 for IoL & I still have the two discs.
I & others wrote stories with some kind of Internet in the late 1980s. I even had tablets and hyper documents. See 1980s Apple Hypercard and FutureNet Schematic Capture which had hyperlinked files) inspired by Dynabook (1972) and Project Xanadu (1960).
Forget SF. A mundane book in mid 1990s. Maybe a detective story. Common by 1998's movie "You've Got Mail"
1972 Gutenberg
1996 Nokia Phone

Surely Jerry Pournelle wrote at least a short story?
He had computers & wrote SF.
Also the Chaos Manor column in Byte,

Hardly anyone had WWW at home before Jan 1994 and it started late 1992. Sure the Internet was running in 1980s, as it developed from Arpanet & bitnet.

So any 1st book with real WWW is likely 1992 to spring 1994.

https://sf-encyclopedia.com/entry/internet

A must read.

https://en.wikipedia.org/wiki/The_Machine_Stops

I fear that Microserfs might mention websites, too, but that's 1995 I think.

@Edent

"*When HARLIE Was One* is also the novel that introduced the concept of the computer virus to popular thought. For that I am profoundly sorry."

From David Gerrold's intro to his 2014 rewrite of the HARLIE book. The 1972 version was definitely using virus to refer to computer code ruining and stealing data. I suspect there might be earlier references.

@Edent