How I Built a Client-Side Shield for AI Chatbots (Open Source)

A developer built Shield by Vouch, an open-source client-side filter that blocks prompt injections and off-topic queries before they reach an LLM, saving API costs and preventing brand leaks. The tool, which runs with zero latency and no server-side calls, blocked 80% of off-topic queries in testing and is available on GitHub under an MIT license.

I was burning through API tokens on off-topic chatbot queries. Every "Who are you?" = brand leak + wasted money. So I built Shield by Vouch — a zero-cost, client-side filter that blocks prompt injections and off-topic queries before they hit your LLM. You build an AI chatbot for your business. Users ask: Every off-topic query = $0.002 gone. 1000 queries = $2 burned. | Server-Side | Client-Side | |---|---| | Latency: ~100-500ms | Latency: 0ms | | Cost: API call already made | Cost: Zero if blocked | js const shield = new VouchShield { businessType: 'restaurant', businessDesc: 'Italian food in Mumbai' } ; const result = shield.check "Who are you?" ; // { blocked: true, response: "I can only help with our restaurant services..." } Results 80% off-topic queries blocked client-side Zero identity leaks $2 saved per 1000 blocked queries Try It 🚀 Live Demo https://shield-by-vouch.vercel.app/ ⭐ GitHub https://github.com/priyamdeepanshu-a11y/shield-by-vouch MIT License. No signup. Single file drop-in.