Mozart's String Duo No. 1 in G major for violin and viola, K. 423, the first of the two Mozart wrote to complete Michael Haydn's set of six for the Archbishop Colloredo, was written in the summer of 1783. It is in three movements:
1. Allegro, common time
2. Adagio, C major, 3/4
3. Rondeau: Allegro, cut time