Simon Willison’s Weblog

Understanding Bidirectional (BIDI) Text in Unicode. It turns out you need to sanitise user input to ensure there are no unicode characters that switch your site’s regular text to RTL.

Posted 15th March 2009 at 4:37 am

Recent articles

GPT-5: Key characteristics, pricing and model card - 7th August 2025
OpenAI's new open weight (Apache 2) models are really good - 5th August 2025
ChatGPT agent's user-agent - 4th August 2025

bidi 1 cal-henderson 7 filtering 2 security 532 unicode 29 userinput 1

Monthly briefing

Sponsor me for $10/month and get a curated email digest of the month's most important LLM developments.

Pay me to send you less!

Sponsor & subscribe