Keep your screen awake in Chrome — no extension needed.

There are Chrome extensions that do this too, and they're a reasonable choice if you want an always-available toolbar icon rather than a tab you keep open. The tradeoffs run the other way, though: an extension needs installing (and keeps running with elevated permissions in the background across every tab), while this is just a webpage — open it, use it, close it, nothing left behind, nothing to review inchrome://extensions later.

Both approaches end up calling the same underlying browser API, so there's no functional difference in how reliably the screen stays on — it's really a question of whether you'd rather have a toolbar button or a tab.