Background : While leadership training is increasingly incorporated into residency education, existing assessment tools to provide feedback on leadership skills are only applicable in limited contexts. Objective : We developed an instrument, the Leadership Observation and Feedback Tool (LOFT), for assessing clinical leadership. Methods : We used an iterative process to develop the tool, beginning with adapting the Leadership Practices Inventory to create an open-ended survey for identification of clinical leadership behaviors. We presented these to leadership experts who defined essential behaviors through a modified Delphi approach. In May 2014 we tested the resulting 29-item tool among residents in the internal medicine and pediatrics departments at 2 academic medical centers. We analyzed instrument performance using Cronbach's alpha, interrater reliability using intraclass correlation coefficients (ICCs), and item performance using linear-by-linear test comparisons of responses by postgraduate year, site, and specialty. Results : A total of 377 (of 526, 72%) team members completed the LOFT for 95 (of 519, 18%) residents. Overall ratings were high-only 14% scored at the novice level. Cronbach's alpha was 0.79, and the ICC ranged from 0.20 to 0.79. Linear-by-linear test comparisons revealed significant differences between postgraduate year groups for some items, but no significant differences by site or specialty. Acceptability and usefulness ratings by respondents were high. Conclusions : Despite a rigorous approach to instrument design, we were unable to collect convincing validity evidence for our instrument. The tool may still have some usefulness for providing formative feedback to residents on their clinical leadership skills.