Case Study: Dutch Tax Office achieves agile, error‑resistant tax‑rule automation with JetBrains MPS (ALEF)

MPS-Customer Experience

The Dutch Tax and Customs Administration (DTCA) is a large government software consumer that processes over 6 million individual tax returns and 1.1 million entrepreneurs’ returns each year and handles hundreds of billions of euros. Because even small errors in tax calculation can cause enormous losses, DTCA needed a way to safely and quickly translate frequent law and policy changes into correct, auditable calculation logic without long, error-prone handoffs between lawyers, tax experts, and IT.

DTCA built the Agile Law Execution Factory (ALEF) with JetBrains MPS, using a controlled natural language (RegelSpraak) and model‑driven engineering to capture rights, rules, fact patterns and tests as structured knowledge models. ALEF generates FICO Blaze rule code deployed as a decision service on the mainframe, enabling domain experts to edit, refactor and test rules, accelerate legal changes, and reliably scale mass tax calculations while reducing implementation risk.

Dutch Tax Office