Bsrgvty

The campaign I’m preparing is designed to give the illusion of choice via side quests and an open world (not really open), but with a main story line that will be pushed into them sooner or later. The campaign is structured in acts and areas, with each area acting as a sandbox space you can’t really leave, but with an expectation the players will move on to the main plot.

Now, on one side, the campaign will be a lot more fun if the players are not completely aware of this fact and they feel they are free to do whatever they want until certain “events” just push them to go in a given direction. On the other hand, if they behave randomly or fight against the main story line it will ruin the campaign as it is not supposed to be really Sandbox play.

Should I explicitly state to them the type of campaign I’m designing or should I “demonstrate” the type of campaign and hope they’re on board with it?

It’s not a question of etiquette but more trying to decide if I’ll break the suspense by letting them know the general story arc is already on my mind... even if they intuitively already know or suspect it.

Yes, you should discuss it with them.

First, it is important to note that "Sandbox" and "railroad" are more of a spectrum than an either-or proposition. As I understand it, you want to put at least some major events on a railroad and allow a bit more of a sandbox during the temporary stops along the rails.

This is a perfectly valid style of play. When I am a gm, I tend to do something similar with certain major plot points preplanned and enforced. This makes it easier for me to have a deep plot and do planning while still allowing some freedom that goes beyond just shuffling from one combat to the next. When I play, I am willing to accept a certain amount of railroading if it makes my gm's job easier and makes them more inclined to develop a deep plot.

However, I explain ahead of time to my players that certain aspects are pre-ordained and I generally appreciate the same courtesy when I am a player. This is especially pertinent right now because games that are much further towards the sandbox side seem to be the default expectation in many communities of gamers right now.

If your players expect a certain amount of railroading then I expect most will accept it quite nicely or at least have a polite discussion about why they don't like that style. If they run into rails or walls they didn't expect though, it can breed feelings of resentment and helplessness. This is especially true if we are talking about significantly negative events that are pre-ordained.

You haven't provided the details of your campaign, but you can probably have a detailed discussion about where on the sandbox-railroad spectrum your game will fall without spoilers. Even if you find light spoilers are necessary, I think that will still be a worthwhile tradeoff for having the discussion. Your players are likely to be much happier if they go into the game with clear expectations.

Consider the Same Page Tool

As John Grabanski kindly reminded me, the Same Page Tool can be helpful in having this type of discussion with your players, and it can cover several other topics as well that are often best discussed before starting a game, especially if the group has not played together before.

I Have Never Seen GM Style Considered As A Spoiler

On the one hand, you worry about the players' lack of knowledge causing them to act in ways that are not in accord with the conventions of a game which has a pre-determined main plot. This seems perfectly valid to me.

On the other hand, you talk about ruining the "suspense" of whether there is or is not a pre-determined main plot. Critically, you're not worried about them knowing the details of the plot, just whether there is or is not one. In my mind, this is a fundamental disconnect.

Much like genre (high fantasy, gritty fantasy, science fiction, whatever), I've never seen this broad level of GM style considered to be a spoiler.

Your experience may vary, but I do not ever remember playing in a game or running a game where the existence of pre-determined plot arc was any kind of suspense point. At all. Nor have I ever had a player express that concern to me. Even in my earliest days of gaming, I never once sat down at the table thinking, "I hope no one spoils me as to whether this is plotted or sandbox." But I have experienced, as a GM, those unfortunate moments when I let something slip too early and spoiled some detail of the plot/background before its time. (If it's ever happened to me as a player, it slipped past me. But I bet it haunted the GM.)

To the contrary, as a player I generally want to know something about the style of the GM, so that I can determine if we're likely to mesh and so that I act in accordance with the game setup (as you rightfully point out.)

I always share this information with my players, as well. More than share, I try to gather or build a consensus around the style of game before I'm too far into the design process.

At the risk of belaboring the obvious, I'll make one final related point: you can share the existence of plot (or, the degree of plotted-ness, since it is not really either-or) without revealing the details of the plot. In my experience, you can even reveal quite a bit about the type of plot ("Everybody up for a good classic Defeat The Dark Lord style game? Cool!") without ruining the suspense of the game in any meaningful way.

So, yes, discuss with your players is my strong advice.

Yes, talk to them

but plan what to say and how to phrase it beforehand, so you find a good balance between spoling and saying nothing.

The campaign is structured in acts and areas, with each area acting as a sandbox space you can’t really leave

That can be phrased as " the individual chapters are sandboxes for themselves, but I may railroad the transition" [that's still badly phrased tho, you can do batter]

Also tell them that yes, there is an already-planned main story and you expect them not to fight against it.

That approach should cover your concerns and inform the players of what to expect without spoiling them