Shulchan Arukh, Orach Chayim 112/שולחן ערוך·אורח חיים קי״ב

1That One Should Not Interrupt [the Amidah], Neither In The First Three [Blessings] Nor in the Final Three. Containing 2 Se'ifim: One should not ask for one's needs in the first three [blessings of the Amidah] nor in the final three. And this is specifically [regarding] the needs of the individual, but [for the] needs of the community, it is permitted.

2One should not say liturgical poems nor a "krovetz" (meaning "krovot l'Yotzeir" [close to the blessing of Yotzeir Or], and some say it is an acronym for "Kol Rina Vi-shua B'ohalei Tzadikim" [Psalms 118:15]) during the prayer [i.e. Amidah]. Gloss: And there are those who permit [them], since they are [considered] needs of the public (the Rosh; Tosefot; the Ri; and the Ran at the beginning of the last chapter of Tractate Rosh Hashana; and Hagahot Maimoni, chapter 10; and the Tur), and such it is practiced in all places to say them.