The published dictionaries only seem to have the noun form. In computing, it's common to use this as a verb, with the meaning you intend.

I don't know a word other than increment, which as you say is not well known outside the technical sphere.

@ColinFine I think the issue is more that outside programming it carries the meaning of "increase by a small amount" or simply "increase" - so even people eho know the word in other contexts won't read it as intended

But the full Oxford English Dictionary explicitly mentions the increase by 1 sense in their definition 4b (Mathematics and Physics) - A small (or sometimes infinitesimal) amount by which a variable quantity increases (e.g. in a given small time); spec. the increase (positive or negative) of a function due to a small increase (esp. of unity) in the variable. If some of your readers don't understand the usage, it's their problem, not yours.

Is is a dose of magic in the game?

"add one" has fewer letters than "increment" and is less ambiguous. I'd expect to see "increments by one" if there was any doubt about the size of change.

@FumbleFingers definition 4b is not exactly high up the list. Not everyone in the gaming world is familiar with computer science or applied mathematics terms. I imagine for many laypeople "each boost increment quantity" sounds jargon because it is jargon.

I can neither think of nor find a reliable answer in maths, computing, physics or general usage. An increment is an increase, an addition, a gain and so forth (see Cambridge and Merriam-Webster). Although it may mean a unitary increase in some contexts (as recognised by Oxford) that is not its general meaning, and increments may be any number or defined quantity. To avoid any doubt the increment must always be quantified or made plain from context. An incremental scale is one that increases by regular amounts, but the amount is not necessarily unity.

@Mari-LouA: You don't need to be a computer scientist to understand that the "next number" displayed on a ticket dispenser (as used for queue management) increments every time another person takes a ticket. Someone would surely say something if the number didn't change, or went up by more than 1. If the amount of the increment isn't 1, we usually call it increasing, not incrementing.

@FumbleFingers "If some of your readers don't understand the usage, it's their problem, not yours." – I was always taught that writers should try to write in a way that their readers will understand. To my knowledge, most people aren't familiar with the "add one" sense of the word "increment," so someone writing for a common audience should avoid it. No sense in using a mało znany word instead of a common one.

Is there some reason why you don't simply word it, "each boost adds one to magic"? Finding a different word (I mean, if you have to find it, how likely is it to be more understandable?) won't magically fix clumsy and confusing syntax.

@TannerSwett: If the OP here really thinks his target readership are that ignorant, he can just append by 1 to his text and not waste our time here.

@ToddWilcox: There's a lot of other bullet-points nearby with a structure like, "For gems, a '1' on boost die doubles quantity", and ideally I wanted those sentences to have the same rhythm ("boost die [one-word-modifier] quantity"). Obviously if I have to make it "adds one to" then that's what will happen.

@Anton That sounds like something you might post as an answer?

Huh. I feel like the use of the word "quantity" is kinda confusing. "For gems, a '1' on boost die doubles quantity"? That's not super clear to me. What quantity? The boost die quantity? The gems quantity? I'm a huge fan of parallel bullet structure, so I'm with you on that. Perhaps rewording all of the bullets is an option if you want the documentation to be most clear.

I'd just reword it: "add the number of boosts to your magic power". Or move it into the Boost section (I'm assuming all boosts act the same way -- each eating boost adds 1 to your eating skill, and so on).

@OwenReynolds: They don't. (See my reply comment to ToddWilcox above.)

TIL "increment" doesn't mean "add one"... Mind blown.

+1 @ "+1"

Tap to add X to your mana pool. Where X is the number of Swamps you control, +1.

@DanielR.Collins I think this is a case where "same rhythm" is too much of a straitjacket on your use of language. Yes, "doubles the quantity" works well if you want to multiply by two. What if you want to multiply by eight? Or divide by three? Or add two? All of these operations are easily expressed, but not in the form "[operates-on] the quantity," at least not in any way most people would recognize.