The Aleppo Codex is a bound manuscript of the Hebrew Bible, written by scribes called Masoretes in Tiberias, Israel, around 930 C.E. They surfaced in Aleppo, Syria, sometime in the second half of the 15th century; preserved nearly intact in a synagogue for centuries, until the 20th century.
The Aleppo Codex belongs to a large “family” of Masoretic manuscripts (MS), which contain vocalization, cantillation marks, and Masoretic annotations. One of the best known manuscripts closely related to the Aleppo Codex is MS Leningrad. Some editions of the Bible are based on MS Leningrad, the best known being the latest editions of Biblia Hebraica.
The Aleppo Codex is considered to be the most authoritative copy of the Hebrew Bible. The Dead Sea Scrolls—which are a thousand years older than the Aleppo Codex and which contain all of Isaiah and some of the Psalms from the Hebrew Bible – lack vowels. The Aleppo Codex features both vowel markings and marginal notations.
Three important editions of the Bible based on the Aleppo Codex, are: 1) The Breuer edition. 2) The edition of the Hebrew University Bible Project. 3) The Keter edition of Miqraot Gedolot, published by Bar-Ilan University Press.
Significantly, both the New International Version and the New Living Translation of the Bible base their Old Testament translations on the Masoretic Text of the Biblia Hebraica.
I assume that since the Masoretic Text and the Biblia Hebraica are of significance to modern English translations of the Bible, and since the Aleppo Codex is considered by many to be the most authoritative copy of the Hebrew Bible, being part of the family of Masoretic MS, then the Aleppo Codex is viewed as important and trustworthy.
Some controversy surrounds the history of the Aleppo Codex and some parts of the Hebrew text are still missing, but the pedigree of the Aleppo Codex seems to be accepted by reputable Bible scholars. I hasten to add, however, that this is only what I have culled from the articles in the links below. Please study them for yourself and form your own conclusions.