I agree with most of what you said, but json's numbers are problematic. For one thing, many languages have 64-bit integers, which can't be precisely represented as a double, so serializing such a value can lead to subtle bug if it is deserialized by a parser that only supports doubles. And deserializing in languages that have multiple numeric types is complicated, since the parser often doesn't have enough context to know what the best numeric type to use is.