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 kirilxd/swe-interview-coach --skill system-design-frameworksgit clone --depth 1 https://github.com/kirilxd/swe-interview-coachWrote 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/kirilxd/swe-interview-coach/system-design-frameworks)<a href="https://agentmods.dev/skills/kirilxd/swe-interview-coach/system-design-frameworks"><img src="https://agentmods.dev/badge/skills/kirilxd/swe-interview-coach/system-design-frameworks.svg" alt="Measured on agentmods" 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 | $0.00097 | $0.04301 |
| Opus 5 | $0.00048 | $0.02150 |
| Sonnet 5 | $0.00019 | $0.00860 |
| Haiku 4.5 | $0.00010 | $0.00430 |
Grade A, and why
system-design-frameworks 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 8d 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 — 258 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design Frameworks
RESHADED framework
Default structure for a 45-60 minute open-ended design question. Budget roughly 10 minutes for Requirements + Estimation, 20-25 for Storage through Detailed design, 10 for Evaluation + wrap-up. Announce each stage transition out loud — interviewers score process, not just the final diagram.
Requirements
- Split functional (what the system does) from non-functional (latency, availability, consistency, durability targets).
- Ask scoping questions before drawing anything: who uses it, what ships in v1, read-heavy or write-heavy?
- Attach numbers to non-functional requirements: "redirect p99 < 100 ms", "99.9% available" — never "fast and reliable".
- Restate the agreed scope and get explicit interviewer sign-off before moving on.
Weak: "A URL shortener — okay. I'll hash the URL, store the mapping in a database, and redirect on lookup."
Strong: "Scope check first: shorten and redirect are v1; custom aliases and analytics are out. I'll assume ~100:1 read:write. Non-functional targets: redirect p99 < 100 ms, 99.9% availability, and no mapping may ever be lost — durability beats freshness here."
Estimation
- Produce three numbers minimum: QPS (read and write), storage growth, bandwidth — each rounded to one significant figure.
- Derive them from stated assumptions (DAU, actions per user per day) so the interviewer can correct your inputs, not your math.
- Use the shortcuts: 86,400 s/day, 1M requests/day ≈ 12 RPS, ~2.5M s/month.
- State peak vs average (peak ≈ 2-3× average) and size for peak.
- Don't skip bandwidth (RPS × object size) — for media-heavy systems it shapes the design more than request count does.
Weak: "It'll be a lot of traffic, so we'll need to scale horizontally from day one."
Strong: "100M DAU × 10 timeline reads/day = 1B reads/day ≈ 12K RPS average, ~30K peak. Writes: 100M posts/day ≈ 1.2K RPS. At ~1 KB per post that's ~100 GB/day of new data, ~36 TB/year before replication."
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.
- 8d ago First seen · 258 lines · 97 tokens per session scan A 25dda5366c98
system-design-frameworks is a skill published in the GitHub repository kirilxd/swe-interview-coach (80 stars, last pushed 1mo ago), licensed MIT. It adds 97 tokens to every session and 4,301 once invoked, about $0.0005 per session on Opus 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 2026-08-30.
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