Doctrine for authoring moo's own surfaces.

Frontmatter

A skill's frontmatter carries name and description; read any shipped SKILL.md for the current key set. The description is one line, and Claude Code caps it at 1024 characters.

No when_to_use. Claude Code reads that key and renders it dash-joined onto the description, but every other agent copies SKILL.md verbatim and never reads it, so the text deciding when a skill fires would be invisible wherever it is installed outside Claude Code.

A condition that follows what the skill does is marked Use when <condition>. — a finite clause, never a bare noun phrase or a bare dash. The key name was what marked the condition as a condition; in one string nothing else does, and an unmarked trailing clause reads as more of what the skill produces. A description may also open with the condition and stop there, where naming the capability would discriminate nothing.

A skill that stays in this repo declares metadata.internal: true. The skills.sh installer walks the tree and offers every SKILL.md it finds; that flag is what it filters on.

Version lives in plugin.json only (DRY). The official Claude Code spec does not allow version in SKILL.md frontmatter.

Sizing

• Size a skill by a deletion pass, never a numeric cap.
• Put branch-specific content in files the skill opens when the branch is taken, and name them where they are needed.
• Decision tables > prose explanations.

Token Efficiency

• Challenge every sentence: "Does Claude need this?"
• Bullets for enumerable items; a paragraph when the point is one connected argument.
• No vague terminology; pick one term per concept.

Skill Design

Phrase design decisions as "X over Y: reason".

Unit choice — behavior inlines at build, data references at runtime; a skill's firing is probabilistic, so behavior that must run every time is a hook:

Composition — name-calls, never imports:

• Skills compose by name: a composer names a move and invokes it with the Skill tool; a body never inlines another body.
• New skill when the cognitive mode changes (clarify WHAT ≠ decide HOW ≠ judge unsupervised work; find ≠ fix). One skill = one mode + one gate.
• Two skills over one when triggers differ; a shared explanation the pair needs lives in this file, which owns skill-design reasoning, not in either skill.
• A body names a sibling in exactly two places: a refusal, and a route — wherever in the body those sit. There the name is the refusal's or the route's content, and a reader without it is stranded.
• Ending over hand-off: a finished run states what is now settled and what is still open, in its own words. Naming who handles it next hardcodes the graph n², so one trigger change edits every sibling.

Output form — bound by what the skill hands back, never by one shared sentence. Plain words is the only part that holds across all three:

A cap counted in lines is a compression budget on a handed-back artifact — replace it. A cap on one turn of a loop is pacing, and the rest arrives on the user's next pull — keep it.

Hook Design

Every hook is a function hook: it reaches the human with no model turn. The API is early access; plugin-authoring and /plugin-types are the reference for every event and call.

• A hook never starts a turn the human didn't ask for: no wake, no $.prompt.submit of its own.
• What a hook finds waits where the human looks next, the band above the prompt, and appears there only while it holds something. Detail unfolds on a press and folds back.
• A hook hands to Claude only on the human's Enter: $.prompt.fill a sentence start they finish, with any bulk added as prompt.submit context.
• Work longer than one dispatch runs unawaited, so the turn's end is never held.
• State lives in $.state (this session) or $.store (across sessions), never in temp files or module variables. A hot reload drops module variables.
• A failure shows once, as a toast, and the event passes on.
• A pane or band is verified on events copied from real session transcripts, one per shape it renders; a synthetic event alone never verifies it.
• One hooks module per plugin; a second part composes into it. A second registration on the same event and matcher in one plugin is dropped silently.

A hook that spawns headless claude -p copies its flag set from hope/hooks/judge.sh, where each flag is commented at the point of use.