[derefr]

What the GP means is that JSON doesn't require an implementation to decode JSON integers as arbitrary-precision integers, to be "conformant JSON."

Therefore, you can't assume that if you pass some JSON through an arbitrary pipeline of JSON-manipulating tools, written in various languages, that your integer values will be passed through losslessly.

Therefore, you just shouldn't use JSON integer values when you know that the values can potentially be large. This is why e.g. Ethereum's JSON-RPC API uses hex-escaped strings (e.g. "0x0") for representing its "quantity" type.