If you have ever worked through a "best free browser games" list and found that four of the ten links were dead, you have met the central problem with this genre: nobody maintains these lists after publishing them.
The failure modes, in order of frequency
- The link is a 404 — the host deleted it and the list never noticed
- The page loads but the game refuses to be embedded, so you get a blank rectangle
- The game loads behind a video ad you cannot skip
- The game is real but needs Flash, or a keyboard you do not have on a phone
The blank-rectangle problem
This one is worth understanding because it is invisible to most link checkers. A page can return a perfectly healthy 200 and still refuse to load inside a frame, because it sends a header telling browsers not to allow it. A checker that only looks at status codes will call that game healthy forever, while every visitor sees an empty box.
If you are assembling your own list, check the framing headers as well as the status code. A game that answers 200 but will not embed is worse than a 404, because nothing ever flags it.
What we do
Every game in our catalogue is checked daily for reachability and verified as embeddable before it is ever added. Games that serve ads inside the frame are screened separately, in a real browser, because ad code is injected at runtime and is invisible to anything that just fetches the HTML.