[logv]

Yes, it analyzes a formula or recurrence relation - sorry to get your hopes up :-D I wish it could analyze source code, but the halting problem says that would be a bit difficult.

I think one could execute source code with varying size inputs to get an idea of a function's growth (assuming the function does halt), but I haven't thought about what that entails

PS: maybe I should have named it BOFAT (Big O Formula Analyzer Tool)

[mhh__]

Surely the halting problem only applies in the general case, i.e. given a ideal enough language you could use heuristics or give results applicable only when in xyz conditions e.g. when these nested for loops are in action it's O(n^2)

[logv]

Yes, this is likely true - I really need to think about it more, though. I don't know how to do static or runtime analysis, so I can't say much about it