The Book of Psalms groups its hundred and fifty poems under several self-declared genres in their own Hebrew superscriptions, mizmor for a song accompanied by instruments, shir for a song, maskil for a contemplative or instructive poem, and tefillah, prayer, for only five: Psalms 17, 86, 90, 102 and 142. Psalm 17 is the first of these, and its content earns the label rather than merely wearing it. Where a mizmor typically opens in praise, Psalm 17 opens as a legal brief: "Hear the right, O Jehovah, attend unto my cry; give ear unto my prayer, that goeth not out of feigned lips." The vocabulary throughout is courtroom vocabulary transposed onto the relationship between the psalmist and God. He asks God to try him, to visit him in the night, to test his heart, and to find nothing amiss, using the technical language of judicial examination rather than of worship.
The climax of the plea, "let my sentence come forth from thy presence," asks explicitly for a verdict, not for comfort or rescue on its own terms, which is what separates a justice petition from the far more common cry for deliverance found elsewhere in the Psalter. Other tefillah psalms share this legal register to varying degrees, but Psalm 17 is the most sustained example of a psalm structured as an appeal for a favourable divine ruling on a specific, contested claim of innocence, brought by a petitioner who has no human court left to appeal to.