Abstract: A slack adjuster check tool includes a holding member formed of flanges to engage a slack adjuster and a retention hook and/or chain to hold the tool in place on a slack adjuster. The retention member is located between the holding member and the handle to allow the user to observe the slack by exerting force on the handle to determine how much freedom of movement there is in the slack adjuster. Openings are provided in the holding member to provide direct access to adjustment heads on slack adjusters.