Setting Manageable Analysis Requirements in Text Act of 2021 or the SMART Act of 2021 This bill requires agencies, when publishing a proposed or final major rule, to include a framework for assessing whether the rule achieves its regulatory objective. An agency must assess a rule in the time frame included in the framework. The assessment must compare the rule's anticipated and actual benefits and costs. The bill defines a major rule as a rule likely to cause (1) an annual effect on the economy of $100 million or more; (2) a major increase in costs or prices; or (3) significant adverse effects on competition, employment, investment, productivity, innovation, health, safety, the environment, or the ability of U.S.-based enterprises to compete with foreign-based enterprises.