RSVP online? But how do I word limited seated on invitation?

On mine I did __ seats have been reserved for you

Like above, state "We have reserved ___ seats in your honor." And fill in the blank.

Plus, online, they won't be able to RSVP for extra people. I'm adding an FAQ page where I address that question.

I have seen invitations that say "adult reception following" indicating that people shouldn't bring children but as far as other guests go, people are just supposed to know that only on the people on the envelope are invited. You shouldn't have to state that in the invitation. One way to give people the hint is to ask for a meal option when they RSVP and they will hopefully understand you are only having meals for the people who RSVP. Other than that, you could put in your FAQ (if you have an FAQ) something about how due to limitations of the venue, you are unable to accommodate extra guests.

Sinc eyou are doing the RSVP's online with weddingwire, it already makes it pretty easy for you because they can't just enter in someone elses name or add a guest. When they put in thier name, they get to choose whether they are coming or not and (if you have it set up) what their food preference is, but there isn't a place to add "plus 1" which is awesome. I don't know how personal you want to get with your invitees, but you can enter in your own text into the RSVP page. You can put in your own wording that the guests will see before they put in their names. Other than that, the ladies above have the right idea, just make sure you fill in the blank!

I know the "what's just one person" mentality well. I used to have friends who thought that if they were invited, then they could bring friends. And well, we ended up just having to be very blunt. Something like "Unfortunately due to venue restrictions, we are not able to accommodate any extra guests." Yes, it violates whatever the etiquette rules are, but it was the only thing that got the job done.

That's another thing, as soon as the issue comes up, handle it. The minute a text/email/phone call/voicemail/your MOH telling you so and so said they were bringing a guest, call up that guest, explain that there was a misunderstanding, the invite was only for you and your wife, we can't accommodate your neighbors.

Something like that, I'm sure you catch my drift.