In 2011, the Institute of Medicine (IOM) (now the National Academy of Medicine) published standards for trustworthy guidelines and recommended that the National Guideline Clearinghouse (NGC) of the Agency for Healthcare Research and Quality clearly indicate the extent to which guidelines adhere to these standards. To accomplish this, the authors developed and tested the NGC Extent of Adherence to Trustworthy Standards (NEATS) instrument. The standards were operationalized as an instrument containing 15 items that cover disclosure of the funding source; disclosure and management of conflicts of interest; multidisciplinary input; incorporation of patient perspectives; rigorous systematic review; recommendations accompanied by rationale, assessment of benefits and harms, clear linkage to the evidence, and assessment of strength of evidence and strength of recommendation; clear articulation of recommendations; external review by diverse stakeholders; and plans for updating. After multiple rounds of feedback from experts on clinical practice guideline development, the external validity and interrater reliability of the instrument were evaluated. For each item, 80% to 100% of survey respondents judged it to be a good measure of the IOM standards. All external stakeholders stated that NEATS was suitable for its intended goal. Interrater reliability for the final NEATS instrument had a weighted κ of 0.73. The NEATS instrument is a focused tool that provides a concise evaluation of a guideline's adherence to the IOM standards for trustworthy guidelines. It has good external validity among guideline developers and good interrater reliability across trained reviewers.