Any script for detecting PCB size or the trace width/spacing
You should normally choose these limits before you begin layout, and set up design rules in your layout tool so that it will warn you if you violate them. Then generate your gerber from layout design files that you know don't violate the rules.

Most fabs (I don't know anything about PCBWay) will have tools that can examine the gerbers you send to check these things and verify manufacturability. Then they'll send you a report indicating the violations and their proposed fixes for your approval (or asking you to confirm you'll pay for the boards even if they are faulty because of a rule violation). A low-cost fab might not provide this service if you use their lowest cost service. Unfortunately these tools are fairly costly and generally not economical to be bought by an individual board designer. I've only worked at one company that licensed this kind of tool in house.