3 Excellent Methods to Add PII Filters to Your LLM Apps: Regex, Presidio, and External APIs Compared

safety #llm 📝 Blog|Analyzed: Apr 18, 2026 02:00•

Published: Apr 17, 2026 21:25

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1 min read

Analysis

This is a fantastic and highly practical guide for developers looking to secure their Large Language Model (LLM) applications against data leaks. By comparing regex, Microsoft Presidio, and external APIs, it offers actionable solutions that take only 30 to 60 minutes to implement. It brilliantly highlights a critical, real-world safety challenge and empowers engineers to build safer, more compliant SaaS platforms with ease!

Key Takeaways

•Users frequently input sensitive information like My Numbers and addresses into LLM prompts, making filtering a necessity.
•Developers can choose from three scalable implementation methods: custom Regex, Microsoft Presidio, or External APIs.
•The guide provides a plug-and-play Python solution that takes under an hour and 100 lines of code to deploy.

Reference / Citation

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"The problem has two layers. The first layer is the risk of sending data to external LLM providers... The second layer is the risk of recording it in your own company's logs."

Zenn LLMApr 17, 2026 21:25

* Cited for critical analysis under Article 32.

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