Reciting Hallel on Rosh Chodesh

 https://torahmitzion.org/learn/reciting-hallel-rosh-chodesh/

Conclusion: On Shloshet HaRegalim (the Three Festivals), hallel is recited, and according to some opinions, this recitation isme’haTorah. In contrast, everyone agrees that on Rosh Chodesh, hallel is a minhag, but the custom of reciting the bracha is not universal. Ashkenazim do recite the bracha, but Edot HaMizrach do not.