Dutch person here.
For weed, the law states a maximum of 5 grams (or 5 plants, if you grow them).
For any 'hard' drugs, such as XTC the legal limit is 0. But if you get caught carrying an amount that is small enough to be considered for personal use, the police usually won't act on it.
If you carry larger quantities than what is considered personal use, it is usually confiscated and you risk a fine (but only if the police has indication that you are selling the drugs).
The weird thing is that the 5 gram rule also counts for the weed dispensary (which are known as 'coffee shops' in NL). So even though it is legal for them to sell the cannabis from their shop, they can't legally buy it from the grower. They aren't even supposed to have more than 5 grams in stock. The growers that supply the shops must also do this illegally, and they are constantly playing cat-and-mouse with the police.
Clearly, the law is ambiguous and both police, growers and dispensary owners are encouraging the government to fully legalize cannabis.