When you build AI-powered applications, the most important code you write has nothing to do with AI. It has to do with data sanitization.

Today, my Serverless Financial Agent was aggressively lecturing me for spending 500€. The catch? I didn't spend it. I transferred it between my own multi-currency accounts using Wise.

The Problem:

My backend was blindly feeding raw transaction arrays to Amazon Bedrock. The LLM saw a -500€ transaction and did exactly what I prompted it to do: it roasted me for bad financial habits. If your context window is fed garbage, the output will be garbage.

The Fix:

I had to build a deterministic sanitization layer before the LLM ever sees the data.…