What do I need to use System Design Interview?

The system to design; Scope; Scale target; Constraints or priorities; Time available; Emphasis (optional).

Is System Design Interview free to use?

Yes — run it free in the browser playground (no API key needed for the sponsored trial, or bring any provider key), or install it into Claude Code, Cursor, ChatGPT and more via npx pm-claude-skills. MIT-licensed and open source.

System Design Interview

Q: How do I know the System Design Interview output is good?

The skill verifies itself against its own quality checks: Clarifying questions are design-changing (not generic filler); Capacity estimates show the arithmetic: DAU → requests/day → requests/sec → storage per record → total storage, so the numbers can be sanity-checked; Every row in the Trade-offs table has a non-empty Trade-off column (no rows where the trade-off is blank or says "none"); At least 2 component deep-dives with technology choices justified.

🔵 Stable🕐 updated 2026-06-08 🔷 SkillSpec L3 pm-engineering

Structure a complete system design answer for interview questions or real architecture sessions. Use when asked to design a system, answer a system design interview question, or architect a solution at scale. Produces a structured answer covering requirements, capacity estimates, high-level design, component deep-dives, trade-offs, and follow-up considerations.

▶ Run it free — no key needed 📝 Grade your existing draft View SKILL.md ↗

What to give it

▸The system to design — e.g. "design a URL shortener", "design a notification service", "design Twitter's feed"

▸Scope — interview prep / real architecture decision / practice run

▸Scale target — rough numbers: DAU, requests/sec, data volume — or "assume typical web scale"

▸Constraints or priorities — e.g. prioritise availability over consistency, minimise cost, low-latency reads

▸Time available — interview context only: 30 / 45 / 60 minutes — skip for real architecture sessions

▸Emphasis (optional) — optional — any area to go deeper on, e.g. "focus on the DB design" or "spend more time on scaling"

✅ The bar it holds itself to

Every skill in this library self-verifies — these are this skill's own quality checks, straight from its definition.

✓Clarifying questions are design-changing (not generic filler)

✓Capacity estimates show the arithmetic: DAU → requests/day → requests/sec → storage per record → total storage, so the numbers can be sanity-checked

✓Every row in the Trade-offs table has a non-empty Trade-off column (no rows where the trade-off is blank or says "none")

✓At least 2 component deep-dives with technology choices justified

✓Trade-offs section is honest (not just benefits of chosen approach)

✓Data flow is described end-to-end for the critical path

⚠️ What it refuses to do

Do not jump to solutions before clarifying requirements — always establish functional and non-functional requirements first

Do not present a design without discussing trade-offs — every architecture decision has costs and benefits that must be acknowledged

Do not use vague capacity estimates — show the actual calculation (QPS, storage bytes, bandwidth) not just "this handles scale"

Do not design for unlimited scale by default — match the design to the requirements stated

Do not skip the data model — a system design without entity definitions and data flow is incomplete

Install

npx pm-claude-skills add --agent claude   # or codex · cursor · gemini · hermes
# or one-line MCP (every skill, any client):
claude mcp add pm-skills -- npx -y pm-claude-skills-mcp

Start with

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Drop this on your blog, docs, or site — it renders a "Run this skill" card:

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<script src="https://mohitagw15856.github.io/pm-claude-skills/embed.js" async></script>

💬 Discussion

System Design Interview is one of 1153 open-source professional AI agent skills — all SkillSpec L3. Try them all in the browser · ⭐ Star on GitHub · Browse the full catalog