Writing the rules of magic or technology so they hold for a whole campaign

Most magic systems fail in the same way. They are described beautifully in the setting document, and then the first time a Player asks "can I just do X?", the answer depends on whoever is narrating at that moment. A rule that bends on request was never a rule.

This post is about writing the rules of your magic or technology so that they survive a long campaign. The technique is simple to state and takes some discipline to apply: write the limits first, write them as statements that can be checked, and put them somewhere the story cannot quietly drift away from.

Start with the cost, not the power

Authors tend to begin with what the magic can do. Fire, healing, flight, a ship that folds space. That is the part everyone enjoys writing, and it is also the part that gives you the least to work with, because power alone creates no decisions.

Decisions come from limits. So write three things for every system, in this order:

1. What it costs. Something is spent, risked or changed each time it is used.
2. What it cannot do. Two or three flat prohibitions.
3. Who controls access. Who can use it, and who can stop them.

Take a made-up example. In a river city, "tidecalling" lets a practitioner move water. The cost is that every working leaves the caster's own body dry and cracked for a day. It cannot create water, only move it. Only members of the lock-keepers' guild are trained, and the guild strips the training from anyone who uses it for private gain.

Notice how much story is already implied. A Player who wants to flood a cellar has to find water that exists. A Player who is caught using it has a guild to answer to. Nothing in those three sentences needed a mechanic.

Write limits as testable statements

"Magic is dangerous" is atmosphere. "Casting leaves the caster physically fatigued and unable to cast again until they rest" is a rule. The difference is that you can read the second one and say whether a given moment of narration obeys it.

A useful check while drafting: for each rule, imagine a Player action that would break it, and ask whether the rule is clear enough that the narrator could refuse or complicate that action. If you cannot imagine the violation, the rule is too vague to enforce.

Keep each rule short and put the consequence inside it. Compare:

• "Spirit-binding is taboo."
• "A bound spirit serves for one season and then leaves, and the binder is barred from every temple for a year."

The second gives the narrator something to do. The first gives it something to say.

Separate the rule from the flavor

Every system has two layers. The rule layer is what is true: costs, limits, access. The flavor layer is how it looks and sounds: the colour of the sparks, the words spoken, the smell of the room afterward.

Keep them apart in your notes. Flavor can vary scene to scene and should, because repetition is dull. Rules should not vary at all. When the two are mixed in one paragraph, a narrator that rephrases the flavor can accidentally rephrase the rule along with it.

How this maps onto Fabulator

Fabulator stores a World Seed's setting as structured World Cards rather than as one long prose document. A magic or technology system is a card with its own fields, including one for costs and limitations. When you clone the seed into a campaign, those cards become that campaign's canon.

Canon is treated as the stable layer. It is distinct from state, which is what is true right now (health, inventory, who is where), and from memory, which is a record of what has happened and decays over time. Your rules sit in canon because they are not supposed to change from turn to turn.

The practical effect for an Author is that a limitation written on a magic card is not just reference material. The design documents describe those limits being carried into the narrator's prompt as world rules, so the narrator is told what the magic costs and cannot do on the turns where it matters. A prose-versus-canon check is part of the intended design as well, so output that contradicts a stated rule can be caught and regenerated rather than shown.

That is why the technique above pays off here. A limit that is short, specific and testable is easy to carry as a field. A limit buried in three paragraphs of lore is easy to lose.

A small exercise

Pick one system in your world and fill in these four lines:

• Cost: what is spent or risked on each use.
• Limit: the one thing it can never do.
• Access: who can use it and who polices it.
• Violation: one Player action that would break the limit, and what the world does in response.

If you cannot write the last line, go back and tighten the limit. If you can, you have enough to build a card around.

Where to build it

If you are comfortable with code, the Creator SDK lets you define rulesets and behaviours that are compiled to WebAssembly and run in a sandbox. If you would rather write narrative content, the authoring tools let you create World Cards, including magic and technology systems, without writing any code. Either way, start with the cost, and let the world enforce it.