Spec driven development
Skill buildmoonshot/skillpacks/skills/engineering/expert/spec-driven-development
A beginner-to-expert curriculum of drop-in skills for Claude Code, Codex, and any coding agent. Copy-paste ready, tested, not a link farm.
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What its author says it does
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Use when starting a substantial feature or change — something that spans multiple files, has non-trivial design decisions, or is expensive to get wrong. Makes the agent write a short spec (goal, approach, key decisions, edge cases) and confirm it before implementing, instead of discovering the design by writing code.
SKILL.md
2.2 KB, as published. Nobody here has run it
Spec-Driven Development
For substantial work, write a short spec and agree on it before writing code. The design decisions are cheapest to change as text, before they're encoded across a dozen files.
Write the spec first
Keep it short — a focused page, not a document. Cover:
- Goal — what this needs to accomplish, in one or two sentences. What does "done" look like?
- Approach — the high-level shape: the main pieces, where they live, how data flows. Enough that someone could predict the file structure.
- Key decisions — the choices that matter, each with a one-line rationale: data model, the library or pattern picked, API shape, where state lives. Note the alternatives you rejected and why.
- Edge cases & failure modes — the inputs and conditions that will break a naive version (empty, concurrent, error, large, malicious). How each is handled.
- Out of scope — what this deliberately does not do, so scope doesn't creep mid-build.
Get alignment, then build
Present the spec and confirm direction before implementing. A wrong assumption caught in the spec costs one sentence; caught after implementation it costs a rewrite. Once agreed, the spec becomes the checklist you build and verify against.
Match the effort to the work
This is for substantial, multi-file, or hard-to-reverse work. A one-file change doesn't need a spec — that's what lightweight planning is for. Don't turn every task into a design doc; reserve this for when the design genuinely carries risk.
Why this matters
The most expensive mistakes are architectural — chosen early, discovered late, and woven through everything by the time they surface. A short spec surfaces those decisions while they're still one paragraph to change, and turns implementation into execution against a plan instead of design-by-accident.