Some have the custom to recite the 13 Attributes of Mercy (13 Midot) while taking out the Torah on Yom Tob. Many Siddurim have this as the standard text, whereas others present it as "Some say." The question is whether such a supplication for mercy is appropriate on a festive Yom Tob,
The Hida (Rabbi Hayim Yosef David Azulai,1724-1807) does not mention this custom in his various discussion of taking out the Torah on Yom Tob. While some authorities conclude that it is not proper to recite this text, others offer somewhat of a compromise. They recommend to read the 13 attributes with the Ta’amim (Cantillation Notes) of the Pesukim, This way, it is not so much a prayer, as it is a reading of a Torah text.
Hacham Ovadia opposed saying this prayer altogether.Hacham Yaakov Moshe Hillel (Contemporary Jerusalem scholar and kabbalist) wrote a lengthy thesis on the subject and concluded that it is not proper to say. Moreover, according to the book Derch Eres, the custom of Aleppo was not to recite the 13 Attributes of Mercy .Although many Shuls do say it, there are Syrian communities today that, in fact, follow this authentic, age-old tradition.
SUMMARY: The custom of Halab is not to recite the 13 Attributes of Mercy when taking out the Torah on Yom Tob.
