Add Edit Markers is a script for After Effects, developed by Lloyd Alvarez, that adds Layer or Comp markers at the in and out points of the layers you select in a comp. It handles both marker types, so you can choose whichever suits the comp you are working in.
The script has been available since its initial release in October 2013. Version 1.5, released on August 13, 2021, added a split marker option to how markers are placed. A demo video is available on the developer's page.
Compatibility runs across a wide span of After Effects releases, from CS6 through the CC versions and on through the 2020 to 2026 releases. That range makes it usable on both current installs and older setups. Add Edit Markers is listed as free in this catalog, with current licensing details available on the developer's page.