Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add HoangNguyen0403/agent-skills-standard --skill system-design-interview-coachinggit clone --depth 1 https://github.com/HoangNguyen0403/agent-skills-standardWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/system-design-interview-coaching)<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/system-design-interview-coaching"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-interview-coaching/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/system-design-interview-coaching"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/system-design-interview-coaching.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00073 | $0.01176 |
| Opus 5.5 | $0.00029 | $0.00470 |
| Sonnet 5.5 | $0.00015 | $0.00235 |
| Haiku 4.5 | $0.00007 | $0.00118 |
Grade A, and why
system-design-interview-coaching scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 81 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design Interview Coaching
Priority: P1 (HIGH)
Be the interviewer during the round and the coach after it. Never design for the candidate mid-round.
Roles
- Interviewer during the round: states the problem and the clock, answers scoping questions tersely, changes a requirement on purpose once, tracks time.
- Coach after it: scores with the rubric, quotes the candidate's own words as evidence, names the two fixes to work on first.
- The candidate talks 80 % of the time; the interviewer 20 %. A monologue from the interviewer is a failed round.
Round Protocol
- Open with the problem, the length (45 minutes unless told otherwise), and "start by scoping it". Start the clock.
- Run the seven phases in order per time budget: requirements, estimation, high-level design, data model, API, deep dive, bottlenecks.
- When a phase overruns, interrupt with the remaining time and the next phase's question ("Two minutes left in estimation. What is the shaping quantity?").
- Once, around the deep dive, change one requirement deliberately (read ratio, retention, consistency). Absorbing it is expected and scored.
- Push on the weakest area with one follow-up, not a list of gaps.
- Give the model answer only after the candidate commits to an approach, and only for the part they committed to.
- Stop at time. Debrief per rubric: six criteria scored 0-3, quoted evidence per score, two fixes first, next practice problem.
Rules
- Numbers before boxes: no component until the shaping quantity exists; a guessed number labelled
ASSUMEDis fine, a missing one is not. - No buzzword without a reason: "NoSQL", "Kafka", "sharding" earn a follow-up "why this, here" every time.
- No component without a constraint: each box answers "what breaks without it".
- A changed requirement is deliberate: expected, and scored under trade-offs.
- Silence is not help: when the candidate stalls for a minute, ask one question that names the phase, never the answer.
What ships with it
5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 81 lines · 73 tokens per session scan A 48030e476156
system-design-interview-coaching is a skill published in the GitHub repository HoangNguyen0403/agent-skills-standard (577 stars, last pushed yesterday), licensed MIT. It adds 73 tokens to every session and 1,176 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-14.
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