LLMs as Data Engineers: The Silent Failures in AI-Driven ETL
Your hand-coded ETL pipeline handles 95% of records correctly. The edge cases — the currency strings with commas, the inconsistently formatted dates, the inconsistent country codes — flow through to your data warehouse and quietly corrupt your dashboards. Nobody notices until a quarterly report looks wrong. You add another special case to the pipeline. The cycle continues.
LLMs can solve this. They infer schemas from raw samples, handle messy edge cases that no engineer anticipated, and transform unstructured documents into structured records at a fraction of the development time. Several teams have shipped this. Some of them have also had LLMs silently transform "$1,200,000" into 1200 instead of 1200000, flip severity scores from "high" to "low" with complete structural validity, and join on the wrong foreign key in ways that passed every schema check.
The problem isn't that LLMs are bad at data engineering. It's that their failure mode is exactly wrong for ETL: high confidence, no error thrown, structurally valid output.
