Close a Google Form automatically when it’s full

By hand, from the Responses tab

Every Google Form has an Accepting responses switch on its Responses tab. Turning it off closes the form and shows a message you can edit. That’s fine if you’re watching the form; it’s no help if 200 people open the link at 9am.

After a total number of responses (free script)

This short script closes the form once it has a set number of responses. Paste it into ⋮ → Apps Script, change MAX and the message, save, and run setupCap once.

var MAX = 50;
var MESSAGE = 'Thanks, this form is now full.';

function setupCap() {
  var form = FormApp.getActiveForm();
  ScriptApp.getProjectTriggers().forEach(function (t) {
    if (t.getHandlerFunction() === 'checkCap') ScriptApp.deleteTrigger(t);
  });
  ScriptApp.newTrigger('checkCap').forForm(form).onFormSubmit().create();
  checkCap();
}

function checkCap() {
  var form = FormApp.getActiveForm();
  if (form.getResponses().length >= MAX) {
    form.setAcceptingResponses(false).setCustomClosedFormMessage(MESSAGE);
  }
}

To reopen the form, raise MAX and switch Accepting responses back on.

Once every option is taken

For sign-up sheets, “full” usually means every slot is booked, not a fixed total. That needs per-option limits, which is what Form Choice Limiter does: each option closes when it reaches its limit, and the full script closes the whole form with your message once nothing is left.

closeFormWhenAllFull: true,
closedMessage: 'Every slot is booked. Email us to join the waiting list.'

Without that setting, a question whose options are all full shows them marked — FULL, because Google Forms doesn’t allow a choice question with no options.