[jillesvangurp]

Depends on the language. On the JVM you are fine. With Javascript, doing math on big numbers is probably going to end in tears unless you know what you are doing. Either way, have some tests for this and make sure your code is doing what you expect.

Encoding numbers as string because you are using a language and parser that can't deal with numbers properly (even 64 bit doubles), is a bit of a hack. Basically the rest of the world giving up because Javascript can't get its shit together is not a great plan.

[wruza]

Accounting for the lowest common denominator that has a huge share in it is always a great plan. Every trading platform out there uses "+-ddd.ddd" format, even binary-born protocols completely unrelated to js used it since forever.