Technically, JSON enforces a specific numeric precision by enforcing that numbers are stored as JS-compatible floating point numbers with its associated precision.

Other than that, the best way to go if you want to have a specific precision is to cast to string before serialisation.

Cuelang: https://cuelang.org/docs/reference/spec/#numeric-values

Implementation restriction: although numeric values have arbitrary precision in the language, implementations may implement them using an internal representation with limited precision. That said, every implementation must:

• Represent integer values with at least 256 bits.
• Represent floating-point values with a mantissa of at least 256 bits and a signed binary exponent of at least 16 bits.
• Give an error if unable to represent an integer value precisely.
• Give an error if unable to represent a floating-point value due to overflow.
• Round to the nearest representable value if unable to represent a floating-point value due to limits on precision. These requirements apply to the result of any expression except for builtin functions, for which an unusual loss of precision must be explicitly documented.