Editing Help:Edit summary (section)

===The 500-character limit===
The limit of 500 characters is an approximation. The actual limit is 500 [[Unicode codepoint]]s. Most characters occupy one codepoint, but some characters like those with [[diacritic]]s or [[emoji]]s may consist of more than one codepoint. The limit of 500 codepoints includes the section title marker (and the associated <code>/*&nbsp;&nbsp;*/</code>) and also any wiki markup that may be present. 

For editors who have JavaScript enabled, there is a script included with the page that monitors the codepoint-length of the summary and prevents entering summaries longer than 500 codepoints (both in "Edit source" and in Visual editor). A count is displayed at the right-hand end of the text entry field, showing the number of unused codepoints. When JavaScript is disabled, this safeguard can't function and the only protection is the browser's limit of 500 characters, which may overflow the 500-codepoint limit as a result of any characters that are represented by more than one codepoint.

When the edit is done by a bot, through an external tool (such as [[WP:AWB]]) or through some user script or gadget, it's the responsibility of the tool or script to safeguard against overflowing this limit. In any situation where more than 500 codepoints are entered for the edit summary, the summary is truncated to 500 codepoints when the revision is published.