SDET is highly skilled resource with development as well as testing skills, on the other hand tester is involved in preparing and executing the test cases either manually or by automation. Moreover, Testers are resources with limited programming skills and they are much focused on functional testing (black box testing) whereas SDETs are skilled resources with good programming skills and do the job of tester (white box testing) as well as developer in test automation.

SDET can participate in test automation tool development and may make it for generic use. Testers are not expected to develop test automation tools, they may use these test automation tool to perform the testing required for their software application or project.