Almost every standard Dutch tenancy agreement carries a no-pets line, and most tenants read it as the end of the conversation. Because a clause and an enforceable clause are not the same thing here, people either give up on an animal or bring one home quietly, both on the strength of an assumption.
A blanket "no pets" line in the contract looks decisive but isn't automatically enforceable in the Netherlands. If it comes to a dispute, a judge weighs the landlord's actual interest — nuisance, property damage, allergies affecting other residents — against the tenant's right to a private life at home, which case law has extended to cover keeping a pet. Crucially, the landlord can't just evict you by pointing at the clause; they'd have to go to court and win that balancing test. Courts have upheld bans in specific situations — a genuinely unsuitable small flat, a dog causing real nuisance, a building with shared corridors and other residents' complaints — so it's not a blank check either. Getting a written agreement or at least a friendly heads-up to your landlord before bringing one home is still the smart move.