Run Timing

@run-at decides when your script executes.

Timing options

• document-start: before DOM is fully parsed
• document-end: after DOMContentLoaded
• document-idle: after load when browser is idle

Example

// ==UserScript==
// @run-at document-end
// ==/UserScript==

const button = document.querySelector('button.buy');
if (button) button.textContent = 'Buy now';

Pick the right timing

• Use document-start for early CSS/patching.
• Use document-end for most DOM edits.
• Use document-idle for heavy or non-critical work.

Debug timing issues

If selectors return null, move later:

• document-start -> document-end
• document-end -> document-idle