Huurcheck – Dutch Rent Checker
An open-source Rust engine that calculates the legal maximum rent for Dutch homes with the official points system (WWS), so tenants can see whether they overpay.
- Pure, side-effect-free rules engine with year-versioned parameters
- Every rule cites its official source; official Huurcommissie cases act as test oracles
- Money handled as integer cents, all text in Dutch and English, no tracking
The problem
In the Netherlands the maximum legal rent of a home follows a points system (the WWS), but the rules are spread across policy documents and change every January and July. Many tenants pay more than they legally should without knowing it.
Approach
- Correctness first: rules come only from official sources (Huurcommissie policy books, wetten.nl, rijksoverheid.nl), and every rule in the code cites its document, section and version date.
- Rust workspace: a pure rules engine with no I/O, separate modules for self-contained homes and rooms (they use different point systems), year-versioned parameters, a CLI and a web front end.
- Testing as the oracle: cases from the official Huurcommissie rent check are fixtures that must pass, plus unit tests per rule and property tests for invariants (more m² never lowers the points).
- Privacy: nothing about users is stored, and every result states that it is an indication only.