Preview vs Run in Google Ads scripts: what is the difference?

Google Ads gives you two ways to execute a script by hand: Preview and Run. They differ in one important way.

Preview

Preview executes the script but does not apply changes to Google Ads entities. Pausing a keyword, changing a bid or adding a negative is recorded on the Changes tab as what would have happened, and the account stays as it was.

Run

Run executes the script for real. Changes are applied, and they appear in the account's change history.

What preview does not protect

Preview only holds back changes to Google Ads itself. Everything else still happens:

• Emails are sent.
• Spreadsheets are written to and files are created in Drive.
• Calls to external services are made.

A script that emails a client or overwrites a report sheet will do so in preview.

A safe way to test

1. Preview on one account first and read both tabs: Changes for what would be modified, Logs for what the script printed.
2. Compare a few of the proposed changes with what you see in the account.
3. If the script writes to a sheet or sends email, point it at a test sheet and your own address for the first runs.
4. Only then run it for real and set a schedule.

Scripts that check for preview

A script can ask whether it is in preview with AdsApp.getExecutionInfo().isPreview() and skip its side effects, such as sending email. Well-built scripts use this instead of a separate "dry run" setting, so that preview behaves the way you expect.

When a script is deployed through chiliad, preview and run work the same way: the loader fetches the code and Google Ads executes it in the mode you chose.