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principle-model-the-domain

Skill2 starsChanged 8 months agoMITView on GitHub

Apply when repeated state conditionals reveal a missing domain model.

We split this skill into the rules it gives an agent

1 rule. 1 is common, 0 are distinctive, and 0 are very specific to this project.

  • 1

    Common

    Most of the 42 edited versions we read keep these.

  • 0

    Distinctive

    This author's own choices. Worth a look.

  • 0

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Common:

    Do not force an abstraction.

    line 33

“Common” is measured: kept by at least 6 in 10 of the 42 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Model the Domain

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:

  • A state machine instead of scattered booleans, phases, or lifecycle checks.
  • A typed object/model instead of loose parameters or repeated shape assumptions.
  • A map, registry, lookup table, or discriminated union instead of branching spread across files.
  • A reducer or command/event model instead of ad hoc state mutations.
  • A module organized around one body of domain knowledge instead of a sequence such as load, validate, transform, and save. Execution order is not ownership.
  • A small module boundary that gathers repeated behavior, ownership, or invariants.
  • A queue, cache, index, graph/tree, or normalized collection where the data access pattern calls for it.
  • Any other structure that fits. When none fits, work out what the code must never allow and how the data gets read, then find the structure that encodes exactly that.

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.

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