The short answer
Single player web games can be static files. Multiplayer needs running servers, synchronised state, authority over what is true, and someone responsible for what players say to each other.
That is a large step. Check whether asynchronous competition gets you most of the benefit first.
Asynchronous first
- Leaderboards and personal bests
- Challenge a friend and compare results
- Turn-based play with no waiting
- Shared puzzles where everyone gets the same daily challenge
- Replays of another player's attempt
Most of the social pull of multiplayer comes from comparison, not from simultaneous presence. Comparison is dramatically cheaper to build and run.
What real-time actually requires
| Concern | Implication |
|---|---|
| Persistent connections | Servers running continuously |
| State authority | Server decides truth, client predicts |
| Latency handling | Design must tolerate delay |
| Cheating | Never trust the client |
| Matchmaking | Poor at low player numbers |
The last row is the practical killer for a new game. Real-time multiplayer with few concurrent players is an empty lobby, which is worse than no multiplayer.
Moderation is an obligation
- Decide whether players can communicate at all, and how.
- If there is chat, have reporting and a response process.
- Filter names as well as messages.
- Be clear about age, because that changes what is required.
- Keep records sufficient to act on a report.
The simplest answer is frequently to allow no free text at all. Predefined messages or emotes remove most of the risk and most of the cost.
Cost the running, not just the build
Multiplayer converts a one-off build cost into a continuing operational one: servers, monitoring, moderation and support. Budget for that before committing.
A game that becomes unaffordable to run six months after launch is a worse outcome than one that shipped without multiplayer.