"Jar of Hearts" has been described as an autobiographical song for Perri, recalling an ex-boyfriend who wanted to reconnect after a tough breakup.[8] Seeing writing duties by the song's performer Christina Perri,[clarification needed] additional writing is seen by Drew Lawrence and Barrett Yeretsian; production by the song's writers Barrett Yeretsian and Christina Perri[clarification needed]. "Jar of Hearts" is a rock-oriented tune that is about shunning the continued advances of a former flame who was ungrateful while together, yet now wants to rekindle a failed romance.[9]Lyrically the ballad revolves around an ex of Perri's, who sings personal lyrics.[6] In a blog by the artist,[6] Perri described that the song came from true experiences, stating "I wrote the song after I went home to Philadelphia for the holiday last December. I sat in my childhood bedroom and hid from the boy (with the jar of hearts) who wanted to see me. My heart wanted to see him, my head knew better. I couldn't take one more break so I wrote the song instead."[10]According to the sheet music published at Musicnotes.com by Hal Leonard Corporation, "Jar of Hearts" is a moderate piano-rock song pacing in common time, written in the key of C minor.[11] Perri's vocals range from the notes Eb3-C5 as she sings to the score of pianos and chords.[11] The song consists simply of a piano melody and delicate strings.[6] Additionally described as a wrenching, string-drenched ballad, the song features "angsty, unvarnished piano rock."[3] Perri stated that she does not know how to read or write music, but knew how to perform certain piano chords, which were used in the song. In the singer's personal blog she released the piano chords of the entire song. The verse of the song is played in the chords Cm Eb Bb Fm; the pre-chorus in Fm Ab Eb Bb Fm Ab Bbsus; the chorus in Eb Bb Cm Ab (Abm) end with: Eb; the bridge in the chords Cm (right hand) Walk down C, B, Bb, A (bass note) Ab G; and the outro finishes the song in the chords Ab B F.[10]