The full form
Lord Jesus Christ, Son of God, have mercy on me, a sinner.
Shorter forms
All are traditional. Use whichever can be repeated without effort.
Lord Jesus Christ, have mercy on me.
Jesus, mercy.
Also known as Lord Jesus Christ, Son of God, have mercy on me
One sentence, repeated slowly, often in time with the breath. It comes from the desert monks of the fourth century and is the whole of the Gospel compressed into twelve words.
Lord Jesus Christ, Son of God, have mercy on me, a sinner.
All are traditional. Use whichever can be repeated without effort.
Lord Jesus Christ, have mercy on me.
Jesus, mercy.
Ancient Eastern Christian tradition; cf. Catechism of the Catholic Church, 2667
This text is in the public domain. About these texts
The prayer of sorrow for sin, said at the end of Confession and traditionally each night before sleep. Both the long and short forms are given.
Written by Blessed Charles de Foucauld, who spent fifteen years in the Sahara with almost nothing to show for it. For the stretches when a person has genuinely run out of plans.