[int_19h]

It's tolerated because the JSON spec explicitly allows it:

   This specification allows implementations to set limits on the range
   and precision of numbers accepted.  Since software that implements
   IEEE 754 binary64 (double precision) numbers [IEEE754] is generally
   available and widely used, good interoperability can be achieved by
   implementations that expect no more precision or range than these
   provide, in the sense that implementations will approximate JSON
   numbers within the expected precision.  A JSON number such as 1E400
   or 3.141592653589793238462643383279 may indicate potential
   interoperability problems, since it suggests that the software that
   created it expects receiving software to have greater capabilities
   for numeric magnitude and precision than is widely available.

   Note that when such software is used, numbers that are integers and
   are in the range [-(2**53)+1, (2**53)-1] are interoperable in the
   sense that implementations will agree exactly on their numeric
   values.

And yes, this is completely insane for a format that supposed to be specifically for serialization and interop. Needless to say, the industry has enthusiastically adopted it to the point where it became the standard.

I miss XML these days. Sure, it was verbose and had a bunch of different and probably excessive numeric types defined for XML Schema... but at least they were well-defined (https://www.w3.org/TR/xmlschema-2/#built-in-datatypes). And, on the other hand, without a schema, all you had were strings. Either way, no mismatched expectations.