Records every closed trade with its real costs: commission, swap and net result.
Computes your stats and shows which pairs, sessions and hours work for you.
Manages your open trades: break even, trailing and partial closes.
Enforces the trading plan and limits you set yourself.
What it does not do
It does not open trades. Ever. It is not a trading bot and will not become one.
It cannot stop you from sending an order: MetaTrader does not allow that. What it does is close it as soon as it appears, if it goes against your plan.
It does not protect with MetaTrader closed. With the program shut, nobody is watching.
It guarantees nothing. A market gap jumps over any stop, yours and ours.
When Onyx Guardian closes a trade you opened outside your hours, that entry cost you the spread and commission. Not a bug: it is the price of breaking your own plan, and it is there on purpose.