Apps Script Triggers

Simple vs installable

	Simple (onOpen, onEdit, onInstall, onSelectionChange)	Installable (ScriptApp.newTrigger(...))
Registration	Automatic — GAS calls the global function by name	Explicit — created programmatically or via the Triggers UI
Runs as	The user currently viewing the file, with their authorization	The user who created the trigger, with that user's authorization, regardless of who triggers it
Can call authorized services	No — no UrlFetchApp, no most advanced services, no services needing OAuth consent	Yes — full access to whatever the installing user has authorized
Typical use	UI-only reactions (build a menu, format a cell)	Anything that calls an external API, sends email, or must run reliably regardless of viewer permissions

If a simple onEdit needs to call UrlFetchApp or MailApp, it will silently fail or throw a permission error — convert it to an installable trigger instead. This is the most common "trigger works when I test it, breaks for other users" bug: the simple trigger works for you (the owner, already authorized) and fails for a viewer/editor without those grants.

Event object shapes

Trigger	Event object fields
onEdit	{ range, oldValue, value, source, user, authMode } — oldValue/value are only present for single-cell edits with a scalar value; multi-cell pastes omit them (check range.getNumRows()/getNumColumns() instead of assuming value exists)
onChange	{ changeType, source, user } — changeType is one of EDIT, INSERT_ROW, INSERT_COLUMN, REMOVE_ROW, REMOVE_COLUMN, INSERT_GRID, REMOVE_GRID, FORMAT, OTHER
onFormSubmit	{ values, namedValues, response, source, triggerUid } — namedValues maps question titles to arrays (a checkbox question yields multiple values)
Time-driven	No event object — the handler runs with no arguments

Quotas

Execution time limit: 6 minutes per invocation, for both consumer and Google Workspace accounts as of this writing. Trigger-specific caps (total triggers per user/script, total trigger runtime per day) differ by account type and change without notice — don't trust a number pasted into a skill, including this one. Query the live docs instead of the number above:

../apps-script-services/scripts/check-quotas.sh "Trigger"
../apps-script-services/scripts/check-quotas.sh "runtime"

(The script lives in the apps-script-services skill, which owns the broader quota reference — see that skill if it isn't installed alongside this one.)

Registering installable triggers without duplicating them

ScriptApp.newTrigger(...).create() is not idempotent — running the setup code twice creates two triggers calling the same handler, which then runs twice per event. Always check existing triggers by handler function name before creating:

function ensureEditTrigger(spreadsheetId: string, handlerFunctionName: string): void {
  const alreadyExists = ScriptApp.getProjectTriggers().some(
    (trigger) => trigger.getHandlerFunction() === handlerFunctionName,
  );
  if (alreadyExists) return;

  ScriptApp.newTrigger(handlerFunctionName)
    .forSpreadsheet(spreadsheetId)
    .onEdit()
    .create();
}

Run this kind of setup once, from an explicit "install" action (a menu item, onInstall, or a setup script) — not from inside the trigger handler itself.

Verification

• Any handler calling an authorized service (UrlFetchApp, MailApp, advanced services) is registered as an installable trigger, not left as a simple trigger.
• Trigger setup code checks ScriptApp.getProjectTriggers() before creating a new one.
• onEdit/onChange handlers don't assume event.value exists — they branch on event.range dimensions first.