Which marks are removed
Tashkeel, or Arabic diacritics, are small signs above or below letters that show short vowels and pronunciation. The tool removes the three short vowels fatha, damma and kasra (the harakat); the three tanween marks for -an, -un and -in; shadda, which doubles a consonant; sukun, which marks the absence of a vowel; and the superscript or dagger alef written in words such as هٰذا. Under Quranic marks it also removes the small annotation signs used in the Mushaf and the extra vowel signs used for other languages written in Arabic script. The code points follow the Unicode Character Database.
Letters stay as they are
Hamza and madda are part of the letters أ إ آ ؤ ئ, so they are kept. If a text was typed with a separate combining hamza after a bare alef, the tool first joins them into one letter, as the Unicode standard does with NFC normalisation, so أحمد stays أحمد instead of turning into احمد. Numbers, Latin text and punctuation pass through unchanged, so mixed Arabic and English documents are safe to clean.
Tatweel and letter normalising
Tatweel (ـ), also called kashida, stretches a word for design and justification, as in سـلام. It carries no meaning, so you can remove it, but it is off by default because some designs use it on purpose. The four letter options go further and change spelling: أ إ آ ٱ become ا, ؤ becomes و, ئ becomes ي, ة becomes ه, and ى becomes ي. That is how search engines and databases often match words written in different ways, but it is not correct spelling, so keep these off for text that people will read.
When removing tashkeel helps
Diacritics make search harder: a search for محمد will not find مُحَمَّد in many programs. Removing them helps when you build a search index, clean data for a spreadsheet or database, compare two versions of a text, prepare subtitles, or paste Arabic into a system that shows marks badly. When quoting the Quran or other texts where vocalisation matters, keep the full vocalised text from a trusted source and use the stripped copy only for search or indexing.
Removing, not adding
This tool only removes marks. Adding the right tashkeel to plain Arabic text needs an understanding of grammar and meaning, and automatic vocalisers make mistakes, so we do not offer one. If you need fully vocalised text for teaching or publishing, ask an Arabic teacher or editor to check it. Everything here runs in your browser, so nothing you paste is uploaded.