Inspired by pantherbane's creation magnet grappling hook and having done a bunch of CAT6 cabling in my house recently, I thought this would've come in handy. Provided are STLs for both parts together and separate.
In addition to the printed parts, you'll need some length of string and 1 5x10mm magnet. The magnet requires a press fit, I used channel locks to press the magnet into the printed housing (see attached image). NOTE: this fit may not work so well with PLA, I used PETG and would recommend using PETG or ABS.
The tool is used to run cables up vertically behind walls. Just drill a hole at the bottom where you want your cable to enter the wall and at the top where you want it to exit, then put a screwdriver or something metal at the bottom and run the fishing magnet down the top until it makes contact with the screwdriver. Remove the screwdriver with the magnet attached from the bottom, tie on the cable you want to pull through and pull it through the top.