Contribution: This concept article shows how the mathematical competencies research framework (MCRF) can guide the design of rubrics to assess engineering mathematics tasks. Practical guidance is given for engineering mathematics educators wanting to create effective rubrics that support student learning and promote academic success. Background: The authors argue that including some rubric-assessed tasks can help students cope better with mathematically challenging concepts. By making explicit the mathematical competencies needed, students may make better use of mathematics concepts outside of mathematics classes. Research Question: What are the design principles for using rubrics to develop mathematical competencies in a way that enables engineering students to voice their values? Methodology: Literature on rubric design was combined with the MCRF and engineering graduate attributes to design rubric principles for tasks involving mathematics competencies. Findings: A general rubric is presented, aligned to six mathematical competencies, with an example of a task and rubric for analyzing ac circuits with complex impedance on GeoGebra. By giving room for students to voice what they value, the rubric design helps to address the challenge of inclusion.