The Keymaster perk in Skyrim is mathemati­cally useless

I recently reverse-engineered the formula behind the pickpocket success rate in Skyrim. One of the Pickpocket perks in the game is called "Keymaster", which makes pickpocketing keys "almost always works", and which which I described as "maybe the most worthless perk in the game". Now that we have the formula, we can prove that it's mathematically useless.

<del>Maybe</del> <i>Definitely</i> the most worthless perk in the game.

How it works

The perk is defined in the Skyrim.esm file, and sets the Pickpocket chance to 100% if the item has VendorItemKey. 1 Which is every key, except for four that are missing it: Calixto's Key, two keys related to a Thieves Guild quest (the Red Wave Safe Key and Sabine's Footlocker Key), and Delphine's Secret Door Key. However in the previous post we identified the function that determines pickpocket success, and ApplyPerkEntryPoint happens before the code caps the chance of success, driving it down from 100% to 90% (hence "almost always works").

It also has the prerequisite perk and level requirement. Capping comes after.
Chance is set to 100%... ...and then capped at 90%

Why it doesn't do anything

To unlock this perk you have to already be level 60 in Pickpocket, and have at least one level in Light Fingers, giving you a +20 boost. Because keys have no value or weight, 2 Well, all but one in true Bethesda fashion—the Old Solitude Crypts Key, which has a value of 3 and a weight of 0.15: This affects pickpocket success rate, dropping it by a whopping \(\frac{3}{10} + 4 * 0.15 = 0.9\) percentage points (51% for a normal key vs. 50% for this one), even though the UI doesn't show it because the itemcard.swf file doesn't show stats for ICT_KEY: even if you're trying to pickpocket a key from someone who's level 100 in Pickpocket your odds are \((100 - \frac{100}{4}) + 20\) = 95%, which is already above the 90% floor, meaning the perk won't do anything.

You can technically get the odds lower by contracting Ataxia (bringing your percentage to 76%) but using your perk point to get one more level of Light Fingers would do the same thing as Keymaster, while also applying to other items. Or you could just eat some garlic bread.

  1. Which is every key, except for four that are missing it: Calixto's Key, two keys related to a Thieves Guild quest (the Red Wave Safe Key and Sabine's Footlocker Key), and Delphine's Secret Door Key. ↩︎

  2. Well, all but one in true Bethesda fashion—the Old Solitude Crypts Key, which has a value of 3 and a weight of 0.15: This affects pickpocket success rate, dropping it by a whopping \(\frac{3}{10} + 4 * 0.15 = 0.9\) percentage points (51% for a normal key vs. 50% for this one), even though the UI doesn't show it because the itemcard.swf file doesn't show stats for ICT_KEY:  ↩︎