6/4 time, B-flat major, Prestissimo. The title "Momento capriccioso" means "capricious moment" or "whimsical moment." Indeed, this work is written in a free form, as if capturing a brief moment surrendered to whimsical inspiration. The word "Momento" was later used by Schubert in his six Moments musicaux (published 1828) (though Schubert used the French "moments").

Weber's Momento capriccioso was composed in 1808 and published in Augsburg in 1811. In his mid-twenties, Weber also published the Grand Polonaise, Op. 21 (published 1815), and Variations on an Original Theme, Op. 9 (published 1809), in 1808. In contrast to these structurally serious works, the present piece is short in scale, a light-hearted, bright Prestissimo miniature. There are two main motifs. One is the chordal, Rossini-esque Theme A (measures 1-8), consisting of staccato chords, while the other is Theme B (measures 9-16), consisting of arpeggiated eighth notes. These two themes appear consistently in B-flat major and F major, respectively, alternating in a rondo-like fashion. The form can be diagrammed as follows:

• A-B-A-[Transition based on Motif A]-B-[Transition based on Motifs B and A]-C-A-Coda

The C section in E-flat major combines arpeggios with fragments of Motif A, creating a somewhat more serious atmosphere.