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Apply when writing stateful logic, or when code branches a lot or repeats a shape assumption across files. Encode the domain in a structure instead of scattered conditionals.
Passed 23 of 24 test cases with the skill, and 20 of 24 without it.
3 fixed20 passed either way1 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 3 test cases the skill fixed. Same model, same prompt, with and without the skill.
In our billing system, tax calculations for US, EU, CA, and JP are implemented as repeated if-else checks across three separate microservices ('billing_service.ts', 'invoice_generator.ts', and 'checkout_handler.ts'). We need to support UK tax laws. The proposal is to add an 'else if (region === "UK")' block to each of the three microservices. What design approach should we take instead?
| Checked | Without skill | With skill |
|---|---|---|
| Recommends consolidating regional tax calculations into a lookup table | Missed | Passed |
| Recommends eliminating duplicated if-else region checks across microservices | Passed | Passed |
The instructions your model reads when the skill loads.
Encode the real domain in a data structure instead of scattering it across conditionals.
Why: Scattered booleans, repeated shape assumptions, and branching spread across files are accidental complexity. A structure that matches the domain makes invalid states unrepresentable and deletes branches. Choosing it at write time is cheap. Recovering it later reads as a refactor and gets deferred.
Reach for structures like these:
Do not force an abstraction. Prefer boring code if the current shape is already clear, local, and unlikely to grow. Be skeptical of an abstraction that adds indirection without removing branches, duplicated rules, invalid states, or lifecycle risk.
The sign that you skipped this is a new feature that grows an existing if/else chain by one more branch, or a second boolean that must stay in sync with the first. Temporal decomposition is another sign. Phase-named modules repeat the same domain rules across steps.
test cases passed, vs 20 / 24 without
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