Mr Swinney was speaking at the conference of the EIS, Scotland's largest teaching union, which has backed a ballot on strike action.
EIS general secretary Larry Flanagan warned there should be no return to a "league table approach" to schools.
The minister said new assessments would be "as short as possible".
Speaking at the conference in Dundee, Mr Swinney said: "In one of my first interviews as education secretary, I was asked whether the assessments will be internally or externally marked. I wasn't ready to give an answer then. I am now.
"My answer is this: that's the wrong question and it fundamentally misunderstands what we are doing.
"You all know - because schools already use these systems - that assessment can be delivered using modern technology that provides the results automatically. No additional workload - no high-stakes, externally marked tests. It's not internal or external. It's automatic.
He added: "That is the modern approach to sensible, proportionate, teacher-led assessment that we need and that is exactly what we will work with you to deliver."
Mr Flanagan said he was "encouraged" by the education secretary's approach.
He said: "He reiterated the Scottish government's commitment to investing in education and, in particular, to tackling the poverty-related attainment gap that persists across the country.
"Clearly, as the cabinet secretary himself noted, we will not agree on every issue.
"Delegates in the hall made clear their very real concerns over the Scottish government's plans for national standardised assessments within the National Improvement Framework, and Mr Swinney was left in no doubt that any return to a target-setting, league table approach to education would be fiercely resisted by teachers."
Scotland's Education Secretary John Swinney has told teachers he is "absolutely committed" to reducing their workload.