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Diacritics used in the Arabic script

Arabic script has numerous diacritics, which include consonant pointing known as (إِعْجَام), and supplementary diacritics known as ALA (تَشْكِيل). The latter include the vowel marks termed ALA (حَرَكَات; singular: حَرَكَة, ALA). The Arabic script is a modified abjad, where short consonants and long vowels are represented by letters but short vowels and consonant length are not generally indicated in writing. ALA is optional to represent missing vowels and consonant length. Modern Arabic is always written with the i‘jām—consonant pointing, but only religious texts, children's books and works for learners are written with the full tashkīl—vowel guides and consonant length. It is however not uncommon for authors to add diacritics to a word or letter when the grammatical case or the meaning is deemed otherwise ambiguous. In addition, classical works and historic documents rendered to the general public are often rendered with the full tashkīl, to compensate for the gap in understanding resulting from stylistic changes over the centuries.

The ALA حَرَكَات, which literally means 'motions', are the short vowel marks. There is some ambiguity as to which ALA are also ALA; the ALA, for example, are markers for both vowels and consonants.

The i‘jām (sometimes also called nuqaṭ) are the diacritic points that distinguish various consonants that have the same form (ALA), such as ب, ت, ث, ن, and ي. Typically i‘jām are not considered diacritics but part of the letter. Early manuscripts of the ALA did not use diacritics either for vowels or to distinguish the different values of the ALA. Vowel pointing was introduced first, as a red dot placed above, below, or beside the ALA, and later consonant pointing was introduced, as thin, short black single or multiple dashes placed above or below the rasm (image). These i‘jām became black dots about the same time as the ALA became small black letters or strokes. Typically, Egyptians do not use dots under final ALA , which looks exactly like ALA in handwriting and in print. This practice is also used in copies of the ALA (Qurʾān) scribed by ALA. The same unification of ALA and ALA has happened in Persian, resulting in what the Unicode Standard calls "arabic letter farsi yeh", that looks exactly the same as ALA in initial and medial forms, but exactly the same as ALA in final and isolated forms
سۡ سۜ سۣ سٚ ڛSeveral ways of writing At the time when the i‘jām was optional, unpointed letters were ambiguous. To clarify that a letter would lack i‘jām in pointed text (i. e. , , , , , , , , ), the letter could be marked with a small v or seagull shaped diacritic above, also a superscript semicircle (crescent), a subscript dot (except in the case of ; three dots were used with ), or a subscript miniature of the letter itself. A superscript stroke known as jarrah, resembling a long fatħah, was used for a contracted (assimilated) sin. Thus were all used to indicate that the letter in question was truly and not These signs, collectively known as ‘alāmātu l ihmāl, are still occasionally used in modern Arabic calligraphy, either for their original purpose (i. e. marking letters without i‘jām), or often as purely decorative space fillers. The small ک above the kāf in its final and isolated forms was originally an ‘alāmatu l ihmāl that became a permanent part of the letter. Previously this sign could also appear above the medial form of kāf, when that letter was written without the stroke on its ascender. When kaf was written without that stroke, it could be mistaken for lam, thus kaf was distinguished with a superscript kaf or a small superscript hamza (nabrah), and lam with a superscript l a m (lam alif mim).

Historically Arabic script has been adopted and used by many tonal languages, examples include Xiao'erjing for Mandarin Chinese as well as Ajami script adopted for writing various languages of Western Africa. However, one of the shortcomings of Arabic, especially in comparison to Latin derived scripts or other indigenous writing systems was that Arabic did not have a way of indicating tones. However, in the adoption of the Arabic Script for Rohingya language, known as Rohingya Fonna, 3 tone markers have been developed and used in manuscripts. These tone markers form part of the standardized and accepted orthographic convention of Rohingya. This is the only known instance of tone markers within the Arabic script. Tone markers act as "modifiers" of vowel diacritics. In simpler words, they are "diacritics for the diacritics". They are written "outside" of the word, meaning that they are written above the vowel diacritic if the diacritic is written above the word, and they are written below the diacritic if the diacritic is written below the word. They are only ever written where there are vowel diacritics. This is important to note, as without the diacritic present, there is no way to distinguish between tone markers and I‘jām i. e. dots that are used for purpose of phonetic distinctions of consonants. ◌࣪ / ◌࣭ The Hārbāy as it is called in Rohingya, is a single dot that's placed on top of Fatḥah and Ḍammah, or curly Fatḥah and curly Ḍammah (vowel diacritics unique to Rohinghya), or their respective Fatḥatan and Ḍammatan versions, and it's placed underneath Kasrah or curly Kasrah, or their respective Kasratan version. (e. g. دً࣪ / دٌ࣪ / دࣨ࣪ / دٍ࣭) This tone marker indicates a short high tone .

The process of automatically restoring diacritical marks is called diacritization or diacritic restoration. It is useful to avoid ambiguity in applications such as Arabic machine translation, text to speech, and information retrieval. Automatic diacritization algorithms have been developed. For Modern Standard Arabic, the state of the art algorithm has a word error rate (WER) of 4.79%. The most common mistakes are proper nouns and case endings. Similar algorithms exist for other varieties of Arabic.