Arabic script has numerous diacritics, which include consonant pointing known as iʻjām (إِعْجَام), and supplementary diacritics known as tashkīl (تَشْكِيل). The latter include the vowel marks termed ḥarakāt (حَرَكَات; singular: حَرَكَة, ḥarakah).

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. Tashkīl 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.

Tashkil (marks used as phonetic guides)

The literal meaning of تَشْكِيل tashkīl is 'variation'. As the normal Arabic text does not provide enough information about the correct pronunciation, the main purpose of tashkīl (and ḥarakāt) is to provide a phonetic guide or a phonetic aid; i.e. show the correct pronunciation for children who are learning to read or foreign learners.

The bulk of Arabic script is written without ḥarakāt (or short vowels). However, they are commonly used in texts that demand strict adherence to exact pronunciation. This is true, primarily, of the Qur'an ⟨ٱلْقُرْآن⟩ (al-Qurʾān) and poetry. It is also quite common to add ḥarakāt to hadiths ⟨ٱلْحَدِيث⟩ (al-ḥadīth; plural: al-ḥādīth) and the Bible. Another use is in children's literature. Moreover, ḥarakāt are used in ordinary texts in individual words when an ambiguity of pronunciation cannot easily be resolved from context alone. Arabic dictionaries with vowel marks provide information about the correct pronunciation to both native and foreign Arabic speakers. In art and calligraphy, ḥarakāt might be used simply because their writing is considered aesthetically pleasing.

An example of a fully vocalised (vowelised or vowelled) Arabic from the Bismillah:

بِسْمِ ٱللَّٰهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ

bismi -llāhi r-raḥmāni r-raḥīmⁱ
Or, more accurately matching the diacritics:
bism Allāh al-Raḥmān al-Raḥīm

In the name of God, the All-Merciful, the Especially-Merciful.

Some Arabic textbooks for foreigners now use ḥarakāt as a phonetic guide to make learning reading Arabic easier. The other method used in textbooks is phonetic romanisation of unvocalised texts. Fully vocalised Arabic texts (i.e. Arabic texts with ḥarakāt/diacritics) are sought after by learners of Arabic. Some online bilingual dictionaries also provide ḥarakāt as a phonetic guide similarly to English dictionaries providing transcription.

Harakat (short vowel marks)

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

Fatḥah

The fatḥah ⟨فَتْحَة⟩ is a small diagonal line placed above a letter, and represents a short /a/ (like the /a/ sound in the English word "cat"). The word fatḥah itself (فَتْحَة) means opening and refers to the opening of the mouth when producing an /a/. For example, with dāl (henceforth, the base consonant in the following examples): ⟨دَ⟩ /da/.

When a fatḥah is placed before a plain letter ⟨ا⟩ (alif) (i.e. one having no hamza or vowel of its own), it represents a long /aː/ (close to the sound of "a" in the English word "dad", with an open front vowel /æː/, not back /ɑː/ as in "father"). For example: ⟨دَا⟩ /daː/. The fatḥah is not usually written in such cases. When a fathah is placed before the letter ⟨ﻱ⟩ (yā’), it creates an /aj/ (as in "lie"); and when placed before the letter ⟨و⟩ (wāw), it creates an /aw/ (as in "cow").

Although paired with a plain letter creates an open front vowel (/a/), often realized as near-open (/æ/), the standard also allows for variations, especially under certain surrounding conditions. Usually, in order to have the more central (/ä/) or back (/ɑ/) pronunciation, the word features a nearby back consonant, such as the emphatics, as well as qāf, or rā’. A similar "back" quality is undergone by other vowels as well in the presence of such consonants, however not as drastically realized as in the case of fatḥah.^[1][2][3]

Kasrah

A similar diagonal line below a letter is called a kasrah ⟨كَسْرَة⟩ and designates a short /i/ (as in "me", "be") and its allophones [i, ɪ, e, e̞, ɛ] (as in "Tim", "sit"). For example: ⟨دِ⟩ /di/.^[4]

When a kasrah is placed before a plain letter ⟨ﻱ⟩ (yā’), it represents a long /iː/ (as in the English word "steed"). For example: ⟨دِي⟩ /diː/. The kasrah is usually not written in such cases, but if yā’ is pronounced as a diphthong /aj/, fatḥah should be written on the preceding consonant to avoid mispronunciation. The word kasrah means 'breaking'.^[1]

Ḍammah

The ḍammah ⟨ضَمَّة⟩ is a small curl-like diacritic placed above a letter to represent a short /u/ (as in "duke", shorter "you") and its allophones [u, ʊ, o, o̞, ɔ] (as in "put", or "bull"). For example: ⟨دُ⟩ /du/.^[4]

When a ḍammah is placed before a plain letter ⟨و⟩ (wāw), it represents a long /uː/ (like the 'oo' sound in the English word "swoop"). For example: ⟨دُو⟩ /duː/. The ḍammah is usually not written in such cases, but if wāw is pronounced as a diphthong /aw/, fatḥah should be written on the preceding consonant to avoid mispronunciation.^[1]

The word ḍammah (ضَمَّة) in this context means rounding, since it is the only rounded vowel in the vowel inventory of Arabic.

Alif Khanjariyah

The superscript (or dagger) alif ⟨أَلِف خَنْجَرِيَّة⟩ (alif khanjarīyah), is written as short vertical stroke on top of a consonant. It indicates a long /aː/ sound for which alif is normally not written. For example: ⟨هَٰذَا⟩ (hādhā) or ⟨رَحْمَٰن⟩ (raḥmān).

The dagger alif occurs in only a few words, but they include some common ones; it is seldom written, however, even in fully vocalised texts. Most keyboards do not have dagger alif. The word Allah ⟨الله⟩ (Allāh) is usually produced automatically by entering alif lām lām hāʾ. The word consists of alif + ligature of doubled lām with a shaddah and a dagger alif above lām.

Maddah

The maddah ⟨مَدَّة⟩ is a tilde-shaped diacritic, which can only appear on top of an alif (آ) and indicates a glottal stop /ʔ/ followed by a long /aː/.

In theory, the same sequence /ʔaː/ could also be represented by two alifs, as in *⟨أَا⟩, where a hamza above the first alif represents the /ʔ/ while the second alif represents the /aː/. However, consecutive alifs are never used in the Arabic orthography. Instead, this sequence must always be written as a single alif with a maddah above it, the combination known as an alif maddah. For example: ⟨قُرْآن⟩ /qurˈʔaːn/.

Alif waslah

The waṣlah ⟨وَصْلَة⟩, alif waṣlah ⟨أَلِف وَصْلَة⟩ or hamzat waṣl ⟨هَمْزَة وَصْل⟩ looks like a small letter ṣād on top of an alif ⟨ٱ⟩ (also indicated by an alif ⟨ا⟩ without a hamzah). It means that the alif is not pronounced when its word does not begin a sentence. For example: ⟨بِٱسْمِ⟩ (bismi), but ⟨ٱمْشُوا۟⟩ (imshū not mshū). This is because no Arabic word can start with a vowel-less consonant: If the second letter from the waṣlah has a kasrah, the alif-waslah makes the sound /i/. However, when the second letter from it has a dammah, it makes the sound /u/.

It occurs only in the beginning of words, but it can occur after prepositions and the definite article. It is commonly found in imperative verbs, the perfective aspect of verb stems VII to X and their verbal nouns (maṣdar). The alif of the definite article is considered a waṣlah.

It occurs in phrases and sentences (connected speech, not isolated/dictionary forms):

• To replace the elided hamza whose alif-seat has assimilated to the previous vowel. For example: فِي ٱلْيَمَن or في اليمن (fi l-Yaman) ‘in Yemen’.
• In hamza-initial imperative forms following a vowel, especially following the conjunction ⟨و⟩ (wa-) ‘and’. For example: َقُمْ وَٱشْرَبِ ٱلْمَاءَ (qum wa-shrab-i l-mā’) ‘rise and then drink the water’.

Like the superscript alif, it is not written in fully vocalized scripts, except for sacred texts, like the Quran and Arabized Bible.

Sukūn

The sukūn ⟨سُكُونْ⟩ is a circle-shaped diacritic placed above a letter ( ْ). It indicates that the consonant to which it is attached is not followed by a vowel, i.e., zero-vowel.

It is a necessary symbol for writing consonant-vowel-consonant syllables, which are very common in Arabic. For example: ⟨دَدْ⟩ (dad).

The sukūn may also be used to help represent a diphthong. A fatḥah followed by the letter ⟨ﻱ⟩ (yā’) with a sukūn over it (ـَيْ) indicates the diphthong ay (IPA /aj/). A fatḥah, followed by the letter ⟨ﻭ⟩ (wāw) with a sukūn, (ـَوْ) indicates /aw/.

The sukūn may have also an alternative form of the small high head of ḥāʾ (U+06E1 ۡ ARABIC SMALL HIGH DOTLESS HEAD OF KHAH), particularly in some Qurans. Other shapes may exist as well (for example, like a small comma above ⟨ʼ⟩ or like a circumflex ⟨ˆ⟩ in nastaʿlīq).^[5]

Tanwin (final postnasalized or long vowels)

The three vowel diacritics may be doubled at the end of a word to indicate that the vowel is followed by the consonant n. They may or may not be considered ḥarakāt and are known as tanwīn ⟨تَنْوِين⟩, or nunation. The signs indicate, from left to right, -un, -in, -an.

These endings are used as non-pausal grammatical indefinite case endings in Literary Arabic or classical Arabic (triptotes only). In a vocalised text, they may be written even if they are not pronounced (see pausa). See i‘rāb for more details. In many spoken Arabic dialects, the endings are absent. Many Arabic textbooks introduce standard Arabic without these endings. The grammatical endings may not be written in some vocalized Arabic texts, as knowledge of i‘rāb varies from country to country, and there is a trend towards simplifying Arabic grammar.

The sign ⟨ـً⟩ is most commonly written in combination with ⟨ـًا⟩ (alif), ⟨ةً⟩ (tā’ marbūṭah), ⟨أً⟩ (alif hamzah) or stand-alone ⟨ءً⟩ (hamzah). Alif should always be written (except for words ending in tā’ marbūṭah, hamzah or diptotes) even if an is not. Grammatical cases and tanwīn endings in indefinite triptote forms:

• -un: nominative case;
• -an: accusative case, also serves as an adverbial marker;
• -in: genitive case.

Shaddah (consonant gemination mark)

The shadda or shaddah ⟨شَدَّة⟩ (shaddah), or tashdid ⟨تَشْدِيد⟩ (tashdīd), is a diacritic shaped like a small written Latin "w".

It is used to indicate gemination (consonant doubling or extra length), which is phonemic in Arabic. It is written above the consonant which is to be doubled. It is the only ḥarakah that is commonly used in ordinary spelling to avoid ambiguity. For example: ⟨دّ⟩ /dd/; madrasah ⟨مَدْرَسَة⟩ ('school') vs. mudarrisah ⟨مُدَرِّسَة⟩ ('teacher', female).

I‘jām (phonetic distinctions of consonants)

The i‘jām ⟨إِعْجَام⟩ (sometimes also called nuqaṭ)^[6] are the diacritic points that distinguish various consonants that have the same form (rasm), such as ⟨ـبـ⟩ /b/ ب, ⟨ـتـ⟩ /t/ ت, ⟨ـثـ⟩ /θ/ ث, ⟨ـنـ⟩ /n/ ن, and ⟨ـيـ⟩ /j/ ي. Typically i‘jām are not considered diacritics but part of the letter.

Early manuscripts of the Qur’ān did not use diacritics either for vowels or to distinguish the different values of the rasm. Vowel pointing was introduced first, as a red dot placed above, below, or beside the rasm, 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 ḥarakāt became small black letters or strokes.

Typically, Egyptians do not use dots under final yā’ ⟨ي⟩, which looks exactly like alif maqṣūrah ⟨ى⟩ in handwriting and in print. This practice is also used in copies of the muṣḥaf (Qurʾān) scribed by ‘Uthman Ṭāhā. The same unification of yā and alif maqṣūrā has happened in Persian, resulting in what the Unicode Standard calls "Arabic Letter Farsi Yeh", that looks exactly the same as yā in initial and medial forms, but exactly the same as alif maqṣūrah in final and isolated forms ⟨یـ  ـیـ  ـی⟩.

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. ⟨ح⟩ /ħ/, ⟨د⟩ /d/, ⟨ر⟩ /r/, ⟨س⟩ /s/, ⟨ص⟩ /sˤ/, ⟨ط⟩ /tˤ/, ⟨ع⟩ /ʕ/, ⟨ل⟩ /l/, ⟨ه⟩ /h/), 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 ⟨ح⟩; three dots were used with ⟨س⟩), 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 ⟨ڛ سۣ سۡ سٚ⟩ were all used to indicate that the letter in question was truly ⟨س⟩ and not ⟨ش⟩.^[7] 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 ⟨ك  ـك⟩ 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).^[8]

Hamza (glottal stop semi-consonant)

Although normally it is sometimes not considered a letter of the alphabet, the hamza هَمْزة (hamzah, glottal stop), often stands as a separate letter in writing, is written in unpointed texts and is not considered a tashkīl. It may appear as a letter by itself or as a diacritic over or under an alif, wāw, or yā.

Which letter is to be used to support the hamzah depends on the quality of the adjacent vowels;

• If the glottal stop occurs at the beginning of the word, it is always indicated by hamza on an alif: above if the following vowel is /a/ or /u/ and below if it is /i/.
• If the glottal stop occurs in the middle of the word, hamzah above alif is used only if it is not preceded or followed by /i/ or /u/:
  • If /i/ is before or after the glottal stop, a yāʼ with a hamzah is used (the two dots which are usually beneath the yāʾ disappear in this case): ⟨ئ⟩.
  • Otherwise, if /u/ is before or after the glottal stop, a wāw with a hamzah is used: ⟨ؤ⟩.
• If the glottal stop occurs at the end of the word (ignoring any grammatical suffixes), if it follows a short vowel it is written above alif, wāw, or yā the same as for a medial case; otherwise on the line (i.e. if it follows a long vowel, diphthong or consonant).
• Two alifs in succession are never allowed: /ʔaː/ is written with alif maddah ⟨آ⟩ and /aːʔ/ is written with a free hamzah on the line ⟨اء⟩.

Consider the following words: ⟨أَخ⟩ /ʔax/ ("brother"), ⟨إسْماعِيل⟩ /ʔismaːʕiːl/ ("Ismael"), ⟨أُمّ⟩ /ʔumm/ ("mother"). All three of above words "begin" with a vowel opening the syllable, and in each case, alif is used to designate the initial glottal stop (the actual beginning). But if we consider middle syllables "beginning" with a vowel: ⟨نَشْأة⟩ /naʃʔa/ ("origin"), ⟨أَفْئِدة⟩ /ʔafʔida/ ("hearts"—notice the /ʔi/ syllable; singular ⟨فُؤاد⟩ /fuʔaːd/), ⟨رُؤُوس⟩ /ruʔuːs/ ("heads", singular ⟨رَأْس⟩ /raʔs/), the situation is different, as noted above. See the comprehensive article on hamzah for more details.

Tone markers

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.^[9][10]

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 (/˥/).^[9][10]

The Ṭelā as it is called in Rohingya, is two dots that are placed on top of Fatḥah and Ḍammah, or curly Fatḥah and curly Ḍammah, or their respective Fatḥatan and Ḍammatan versions, and it's placed underneath Kasrah or curly Kasrah, or their respective Kasratan version. (e.g. دَ࣫ / دُ࣫ / دِ࣮‎) This tone marker indicates a long falling tone (/˥˩/).^[9][10]

The Ṭāna as it is called in Rohingya, is a fish-like looping line that is placed on top of Fatḥah and Ḍammah, or curly Fatḥah and curly Ḍammah, or their respective Fatḥatan and Ḍammatan versions, and it's placed underneath Kasrah or curly Kasrah, or their respective Kasratan version. (e.g. دࣤ࣬ / دࣥ࣬ / دࣦ࣯‎) This tone marker indicates a long rising tone (/˨˦/).^[9][10]

History

According to tradition, the first to commission a system of harakat was Ali who appointed Abu al-Aswad al-Du'ali for the task. Abu al-Aswad devised a system of dots to signal the three short vowels (along with their respective allophones) of Arabic. This system of dots predates the i‘jām, dots used to distinguish between different consonants.

• 
  Early Basmala Kufic
• 
  Middle Kufic
• 
  Modern Kufic in Qur'an

Abu al-Aswad's system

Abu al-Aswad's system of Harakat was different from the system we know today. The system used red dots with each arrangement or position indicating a different short vowel.

A dot above a letter indicated the vowel a, a dot below indicated the vowel i, a dot on the side of a letter stood for the vowel u, and two dots stood for the tanwīn.

However, the early manuscripts of the Qur'an did not use the vowel signs for every letter requiring them, but only for letters where they were necessary for a correct reading.

Al Farahidi's system

The precursor to the system we know today is Al Farahidi's system. al-Farāhīdī found that the task of writing using two different colours was tedious and impractical. Another complication was that the i‘jām had been introduced by then, which, while they were short strokes rather than the round dots seen today, meant that without a color distinction the two could become confused.

Accordingly, he replaced the ḥarakāt with small superscript letters: small alif, yā’, and wāw for the short vowels corresponding to the long vowels written with those letters, a small s(h)īn for shaddah (geminate), a small khā’ for khafīf (short consonant; no longer used). His system is essentially the one we know today.^[11]

Automatic diacritization

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.^[12][13] 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.^[14] Similar algorithms exist for other varieties of Arabic.^[15]