Swahili Ajami script refers to the alphabet derived from Arabic script that is used for the writing of Swahili language.
Ajami is a name commonly given to alphabets derived from Arabic script for the use of various African languages, from Swahili to Hausa, Fula, and Wolof.
In Eastern Africa, this script grew from the use of unmodified Arabic Script from the second half of the 19th century onward. The current most widely recognized and acclaimed standard Swahili Ajami Script was proposed in 1997 by the renowned Swahili scholar, Mu’allim Sheikh Yahya Ali Omar.
In the 2010s, there has been work on creating new Unicode characters, on keyboard mapping, and on coding script conversion programs, so that typing in Swahili Ajami Script can become as accessible as typing in Latin Script, so that texts from either script can easily and accurately be converted to the other, and to have a tool digitize and upload historic texts and manuscripts in Swahili for the sake of their preservation. Dr. Kevin Donnelly of SOAS has done an impressive work in doing so and in digitizing historic Swahili manuscripts.
History
Up until the latter half of the 19th century, there was no specific "Swahili script". It was Arabic script with no modification that was used.
Adapting the Arabic script to Swahili phonology
Starting from the later half of the 19th century, continuing into the 20th century, and going on in the 21st century, a process of "Swahilization" of the Arabic Script has been under way by Swahili scribes and scholars. The first of such attempts was done by Mwalimu Sikujua, a scholar and poet from Mombasa. Below are Mwalimu Sikujua's innovations in the process of adoption Arabic script for Swahili phonology:
In his script, he distinguished alveolar [t] and [d] sounds from their dental counterparts which is the norm in Arabic phonology. He did so by adding 4 dots to the letters tāʼ (ت) and dāl (د), creating the letters ٿ and ڐ. This is the same as what was done in Urdu alphabet, where later, the 4 dots evolved into looking like the letter ṭāʾ (ط) The introduction of new letters to represent the sounds [p] and [v] by adding three dots to letters bāʼ (ب) and fāʼ (ف), same as what's been done in Persian alphabet, creating the letters پ and ڤ. For representing aspirated consonants, Mwalimu Sikujua wrote a tiny letter hāʾ (ھ) on top of the aspirated letter. For example, an aspirated alveolar [t] would be written with ه on top of the four dots of the letter ٿ, producing "". For representing prenasalized consonants (sounds such as [ⁿd], [ⁿɡ], and [ᵐb]), Mwalimu Sikujua wrote a tiny letter mīm (م) or nūn (ن) on top or bottom of the letter. For example, the sound [ᵐb] would be written as "بۭ" and the sound [ⁿd] as "دۨ". As explained, Arabic only has vowels for [a], [i], and [u], whereas Swahili has five vowels, the three aforementioned ones and [e] and [o]. For showing the vowel [e], Mwalimu Sikujua modified the existing Kasrah diacritic used for showing [i] (◌ِ), by changing its angle slightly and by adding markings to modify its shape slightly, thus producing a shape resembling "◌̼ ". As for [o], Mwalimu Sikujua inverted the orientation of the existing Ḍammah diacritic used for showing u (◌ؙ), thus representing it with a diacritic resembling "◌ٗ".
The poetry and texts written by Mwalimu Sikujua were published by W.E. Taylor, a Swahili literature scholar of British origin, in the late 19th century. This was probably the first time ever that Swahili in Ajami script was printed and published as opposed to being handwritten. However, the spread of a standardized indigenous variation of Arabic script for Swahili was hampered by the colonial takeover of East Africa by the United Kingdom and Germany. The usage of Arabic script was suppressed in German East Africa and to a lesser extent in British East Africa. Nevertheless, well into the 1930s and 1940s, rural literacy rate in Arabic script as well as a local preference to write Swahili in this script was high. But it's important to note that literacy at the time was in unmodified Arabic script, and not the modified scripts that were thus far proposed by the likes of Mwalimu Sikujua.