It's based on pure JavaScript, without jQuery or something.
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On left you can see text area to input your text. At this time you can input only latin letters.
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Then you have to choose how many letters script should skip during ciphering.
See how Caesar cipher works: here.
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At last click "Cipher" and viola! Encrypted text shows on bottom of the page.
Caesar cipher web application is avalaible in english and polish.