The soprano sax reads like a clarinet
The soprano sax is in B♭ and sounds a whole step below what's written, like the clarinet and trumpet. For a concert C, the player reads a D, and a piece in C major is written in D major.
Flute, oboe or violin parts
Soprano sax players often play melodies written for flute, oboe or violin. Upload that part, pick soprano sax as the target and check the range: the soprano doesn't go below concert A♭.
Frequently asked questions
Does a curved soprano transpose differently?
No, curved or straight, both are in B♭.
What about the sopranino?
It's in high E♭: choose “High E♭”, which transposes like the E♭ clarinet.