Edited: I added a photo of the whole stairs, to see if it looks like it can be fixed or if you all think he needs to start over.
We are currently having our front porch steps and railing rebuilt.
The top step rests right under the porch, resulting in an awkward tiny step up or down.
We've read that there can only be a 3/8" inch difference in rise. Does this small step count as a rise?
That doesn’t meet code, and is flat-out dangerous.
The simplest fix is to lift the entire stringer assembly and raise the grade at the bottom. Or take it apart and do it right from the outset.
I shudder when I imagine that this is being done by a “professional”.
Yes, it counts as a rise.
You need to have the steps redone if you want to be code compliant.
Looks like your top step is ~3" low. You need to make new stringers with the rise being ~3/4" higher.
Or, you can make each rise shorter and have he top tread end rise-distance below the deck. That is, if the rise is 7", the top tread would be 7" below the top surface of the deck.
Can't say for sure because we don't know 1) how many treads there are and 2) what the current rise and run of the steps are.
Don't make it harder than it is.
You need to dismantle it, but you can simply tilt the existing risers to place (the heel of) the top stair flush with the porch.
Then make sure (the heel of) each stair is evenly spaced from the concrete to the porch height.
I say "heel" because if you do this literally, each step will be on a slant. The next step is to use wedge shaped shims to bring up the toe of each step, so the steps are more or less level. But the heels won't change level.
Such wedge-shaped shims are sold at lumberyards for framing doors and the like. You can also cut your own.
Pay extra attention to the bottom step. The rise from concrete to first step needs to be within tolerance of the other steps.
I'll agree with the other answers that this set of stairs is NOT even close to being code compliant. My recommendation (having just done two similar steps on my own home, and researching this topic carefully), is to dismantle it and start again. Get your money back too, if possible. Okay, anyhoo, here is my actual hopeful contribution to the discussion... I found this link VERY VERY helpful:
This one has a calculator that makes the math much easier and provides a stringer-template diagram, that makes it very visual and easy to understand. I used it to create a carboard cutout, so that I could test fit the stringers before cutting any wood: https://www.blocklayer.com/stairs/stairseng.aspx
Stringer Layout ... there are many others.
Watch a bunch of YouTube until you can finally get your head around it.
One more point - I had to adjust the height of the concrete paving stone at the bottom of the stairs so that had the correct riser height as well.
