Agent Skill
Spec Driven Development skill
spec-driven-developmentaddyosmani/agent-skillsskills/spec-driven-development/SKILL.md
Creates specs before coding. Use when starting a new project, feature, or significant change and no specification exists yet. Use when drafting a PRD or requirements document with objectives and scope, or when requirements are unclear, ambiguous, or only exist as a vague idea. Use when a single requirement spans several independently testable capabilities and needs decomposing into a capability map of modules before specifying.
always on
81 tokname + description
once used
2,705 tokSKILL.md body
bundled files
0
installs
62kskills.sh
Install the Spec Driven Development skill
Skills CLI (Claude Code, Codex, Cursor and others)
npx skills add https://github.com/addyosmani/agent-skills --skill spec-driven-development
Claude Code, by hand (all projects)
git clone --depth 1 https://github.com/addyosmani/agent-skills.git /tmp/agent-skills mkdir -p ~/.claude/skills cp -R /tmp/agent-skills/skills/spec-driven-development ~/.claude/skills/spec-driven-development
For one project only, copy the folder into .claude/skills/ in that project instead. The agent picks it up when a task matches its description.
What it costs your context
Agent Skills load in three steps. Tokens counted with the o200k tokenizer; your model's count will differ a little.
| When | What loads | Cost |
|---|---|---|
| Every session | Name and description | 81 tok |
| When the agent uses it | The SKILL.md instructions | 2,705 tok |
| Only if opened | No bundled files | — |
Until it is used, spec-driven-development costs about 17× less than the median MCP server we measured (1,362 tokens on every turn). Installing all 25 skills from addyosmani/agent-skills would load 1,829 tokens of descriptions. Skills vs MCP study
Checks
Our checks found nothing to flag: it follows the Agent Skills specification's naming and size guidelines and doesn't pipe downloads into a shell.
Checked 2026-10-22 · method
What's inside
The headings of its SKILL.md. Read the full file on GitHub.
- Spec-Driven Development
- Overview
- When to Use
- The Gated Workflow
- Phase 0: Scope Check
- Phase 1: Specify
- Phase 2: Plan
- Phase 3: Tasks
- Phase 4: Implement
- Keeping the Spec Alive
- Common Rationalizations
- Red Flags
- Verification
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