So, this sheet is meant to help fantasy world-builders (for any media, not just writing) create the magic systems for their worlds. It is inspired from some character sheets that ask you a series of questions. This sheet may be helpful for you at any stage of the worldbuilding process: whether you're just starting out and need ideas, or you're nearly done and want to make sure everything is consistent. Keep in mind that I'm not technically giving you ideas, just raising questions. This revised version puts more emphasis on definitions than the original.
So, let's start with the term "magic system". A system is a bunch of concepts that work together. Basically, I'll define a magic system as a set of laws for magic. If your world has several kinds of magic that have completely different possibilities (for instance, one kind of magic can do what is completely impossible with another), then you have several systems. If there are many different ways to use magic, but all of them have the same fundamental rules and you feel comfortable saying that it's "the same magic, used differently", you probably have one system. You may, of course, disagree with this definition. If you do, I strongly advise you to come up with your own definition before starting. Note that we're not defining "magic" itself yet.
How to use it
This is not a meme. The goal of this is not to return a set of answers to me. Of course, you are free to post your completed sheet wherever you want - you may even make it into a meme if you really want to, but that's not the original purpose.
In worldbuilding, the only limit is one's imagination. This is why no two worlds will be the same, and similarly, no two magic systems are the same. You are encouraged to alter this sheet to suit your needs, by adding questions, removing those that you think are irrelevant, or in any other way.
Please also keep in mind that if a question reads something like "Is magic A or B?", you may very well answer "It's somewhere in between" or "It's C" or even "It depends on [insert factor here]". Also, when I make a list of examples, this does not mean you have to choose between them. The examples are just suggestions that are meant to clarify the meaning of the question.
If any of my questions seem to contain an assumption, go ahead and question this assumption as well.
Some questions will also raise other questions. Mentioning them all would probably result in a confusing mess, so I had to leave some out. If your answer to a question seems to raise other questions, I encourage you to elaborate, because this will help flesh out your system.
Some aspects of magic and magic systems are intentionally left out. For instance, I did not elaborate too much on the relationships between magic and the society, geography, history, culture(s), science, or religion(s) of your world. This is because your world will likely be different from anything I could imagine, and any questions I could ask without any prior knowledge of your world would be limiting at best, and completely irrelevant at worst (or is that the other way round?). As I said above, let my questions raise more questions, and then answer them.
I - What is magic?
1. How many different magic systems coexist in this world? You may want to have one sheet for each system.
2. Define magic: Is magic the same as the supernatural (what can't be explained with your world's scientific knowledge)? Is magic always supernatural? Is the supernatural always magical? If you answered no to any of the previous questions, what's the difference between magic and the supernatural?
3. From the point of view of the people in your world, is magic an exceptional and rare sight, or is it commonplace?
4. Does magic have one or more name(s)? Where do(es) this/these name(s) come from?
II - Origin
1. Who or what created magic?
2. What for?
3. In what circumstances? (When, if relevant?)
4. To be used by whom?
5. If this was not the main goal, how and why did humans (or your world's main race/species) begin mastering it?
III - Mages
1. Do you have to be gifted in order to use magic? If so, is that gift common or rare?
2. Is it necessary to learn magic in order to be able to use it, and if so, is it difficult?
3. Are there requirements for someone to begin using magic (like some kind of "awakening" or "attunement")?
4. Sociology of magic: Are there any categories of people who have little or no chance of ever being able to use magic? Are there any categories of people for whom it will be easier than for others? Is this because of the necessity to be gifted or because magical studies are not accessible to everyone? Why is that so?
5. Are there any categories of population who can use magic better than others?
6. Is it possible to artificially enable someone to use magic while that person would normally be unable to do it? What about the other way round? What are the limits?
7. Is it possible to naturally gain or lose the gift of magic, if there is one? In what circumstances?
From now on, I will be using the word "spell" to describe an effect that is produced using magic and the phrase "to cast a spell" to refer to the magical act that produces the said effect. If these words are irrelevant in your system (for instance if you have another specific term that means the same thing), or if they mean something else (for example, if they refer to a particular type of magical effect or act as opposed to others), feel free to replace them with something else. I will also use the word "magic-user" to refer to someone who is able to use magic.
IV - Using magic
Introducing the concept of mana or magical energy. I am using both terms to make sure everyone understands what I'm talking about, as "mana" is (originally, at least) a concept specific to certain cultures, and "magical energy" is quite abstract. If you have a better name for this concept - for example, if it has a name in your world, you are encouraged to use it instead of my awkward "mana / magical energy". The following questions are focused on defining what mana or magical energy exactly is in your system.
1. What is the source of mana / magical energy? Is it located within the magic-user or somewhere else?
2. If it is located somewhere else, where is it? Where can one access it from?
3. If the source of magic is within the magic-user, can you run out of it? If so, what happens then?
4. Is it possible to perceive the presence of mana / magical energy? If so, who can do it (all magic-users, some of them, everyone...)? What exactly is perceived? Is it possible to purposefully hide it?
5. Same questions about whether or not someone is a magic-user.
6. Same questions about if magic has been, is being (or will be) used near you.
7. What does one do when using magic? Describe the process(es) of "casting a spell" (producing an effect using magic). Are there different types of magical effects produced using slightly different methods? What does one feel when doing it?
8. If you have to be gifted in order to use magic, can you be "more" or "less" gifted, or is it everything or nothing?
9. What other personal qualities, if any, make someone a good or bad magic-user?
10. Can you be naturally better at some types of magic (within the same system, such as different types of spells) than others? Can you choose to specialize in a certain type of magic? If so, how is that done?
V - Price
1. Does magic have a price (other than using up mana / magical energy, if it does)?
2. Does the use of magic have consequences on the magic-user's health?
3. Is magic believed to harm / disturb the balance of nature or the outside world? If so, in what way? (If not, is it believed to have a positive impact?)
4. Does it actually have any impact of that sort? Is this impact different from what people believe it to be?
5. If anything, what does one sacrifice / "pay" in order to use magic? When (before casting the spell, while doing it, afterwards)? In what circumstances? Is the magic-user aware of this sacrifice when doing it? If not, does the magic-user usually notice it later?
6. Can one avoid paying the price, and if so, how? Can everyone do it? Can you avoid it every time? Can you replace this cost with another kind of cost, and if so, what kind? How does this impact the possibilities of magic-users?
VI - Effects and limits
1. Does magic have one or more "themes" (elemental, for instance)?
2. Is there anything that is technically impossible to achieve using magic?
3. Is there anything that magic-users are forbidden to do using magic? Who forbids it, why, and what are the risks of disobeying?
4. Are there things that could theoretically be done but that no one can actually do? If so, why can no one do it?
5. Are there any secret techniques, or ways to use magic, that are lost, or held secret by a small number of people, or believed to be lost? Are there any spells or types of magic that are known but not used? If so, why are they not used (for example, are they useless, inefficient, frowned upon, out of fashion)?
6. What, if anything, makes certain spells harder to achieve than others? What, if anything, can make one particular spell easier or harder to perform? (Examples: the target's size, physical strength or magical power, the distance between the magic-user and the target, the magic-user's awareness or knowledge of the target, the difference between the desired effect and what should have happened / the chance of the desired effect happening without magic [depending on whether or not fate exists in your world]...)
7. Is it possible for a spell to fail (not counting any mistake on the user's part)? For what reason? Do the magic-users understand this reason?
8. Is it possible to prevent the effect of a spell, and if so, how is it done?
9. Are there side effects of being able to use magic, even when you're not currently using it? (powers that work all the time without any conscious decision from the magic-user, negative or harmful effects, "price" to pay all the time, better or worse resistance to certain magical or non-magical aggressions...)
VII - Items
1. Are any items necessary in order to use magic, such as a magic wand or another item with a similar function?
2. Are any items necessary to cast certain specific spells / use certain types of magic?
3. Can certain items make it easier or harder for someone to cast a spell, or make someone's spells more or less powerful?
4. Are there any items that could render non-magic-users able to use magic? Will there be any limits or restrictions other than the usual limits of magic? Will the usual limits of magic apply here, or are they going to be different?
5. Are there items that have magical properties or powers? (This includes the types of items mentioned in the previous three questions). Who or what gave them these properties? Why? Did they do it intentionally? Or are these properties natural?
6. Is it possible to give an item a magical property or power? (This does not include turning a regular, non-magical item into another regular, non-magical item). Does this property or power have to be permanent, or does it have to be temporary, or does its duration depend on something? If so, what does it depend on?
7. Do magic potions exist? (my definition of a "magic potion": a mixture that has magical properties that the ingredients themselves do not have). How are they prepared?
8. Are there any effects that can only be achieved with potions, or that are much easier to achieve with potions than with any other kind of magic? Why use potions rather than another kind of magic?
9. Can a non-magic-user use a magical item? Will its use (process, effect, consequences) be different from what a magic-user would do?
10. Can a non-magic user prepare a magic potion? Will the potion (preparation, effect, consequences) be different from the same mixture prepared by a magic-user?
VIII - Interactions(If you have more than two systems, you may want to ask yourself these questions for all the possible combinations : will the answers always be the same ?)
1. Can a number of mages unite their efforts or combine their powers? Are there any effects that can only be achieved this way? How is it done? Are there any requirements or limits?
2. Is it possible to borrow someone else's power? How is it done? What exactly is borrowed (mana / magical energy, something else)? Are there any requirements or limits?
3. If there is more than one system of magic, can the various types of magic be combined or work together? Are there any requirements or limits?
4. On the contrary, do the different types of magic sometimes cancel each other? In what conditions? Why?
5. If both of the above are possible, what determines the result?
6. Does being able to use one type of magic make one more resistant or more vulnerable to other types of magic?
7. Is it possible to counter one type of magic with another, or protect oneself from a spell using another type of magic?
8. Does the physical proximity of different types of magic (the proximity of sources of different types of mana / magical energy, the simultaneous casting of two spells using different types of magic in the same location...) have any particular effect? If so, what is it?
9. Can one master more than one type of magic? Can one master all of them? Does this make one better, or worse, at each type of magic? Does this increase, or decrease, the price for using them?
10. Is it possible to use more than one type of magic simultaneously? How is that done?
IX - Perception
1. Do non-magic-users (if there are any) have misconceptions about magic? If so, what are they? Were they spread deliberately, and if so, by whom?
2. Do magic-users themselves have any misconceptions about magic? If so, what are they? Were they spread deliberately, and if so, by whom? Do all magic-users have these misconceptions, or only some of them?