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 05-deepak-patidar/claude-skills --skill system-designgit clone --depth 1 https://github.com/05-deepak-patidar/claude-skillsWrote 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/05-deepak-patidar/claude-skills/system-design)<a href="https://agentmods.dev/skills/05-deepak-patidar/claude-skills/system-design"><img src="https://agentmods.dev/badge/skills/05-deepak-patidar/claude-skills/system-design/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/05-deepak-patidar/claude-skills/system-design"><img src="https://agentmods.dev/badge/skills/05-deepak-patidar/claude-skills/system-design.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 | $0.00084 | $0.01159 |
| Opus 5.5 | $0.00034 | $0.00464 |
| Sonnet 5.5 | $0.00017 | $0.00232 |
| Haiku 4.5 | $0.00008 | $0.00116 |
Grade A, and why
system-design 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 — 60 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design
System design is deciding where data lives, how it moves, and what happens when a part fails. Every box you add must justify itself against the two default answers: "put it in Postgres" and "do it synchronously".
Start from numbers, not from patterns
Before proposing any design, estimate — even roughly:
- Requests/sec at realistic peak (not fantasy scale). Data size now and in 2 years. Read:write ratio. Latency budget for the user-facing path.
- Most business SaaS runs at <50 rps with <50 GB of hot data. One well-indexed Postgres and one app server handles this with room to spare. Design for 10× current load, not 1000×; you will redesign before 1000× anyway, with better information.
State the numbers in the design. A design without numbers is a mood board.
The escalation ladder — take one step only when the current step measurably fails
- Synchronous monolith + Postgres. Correct, debuggable, transactional. Stay here as long as possible.
- Read optimization: indexes → query fixes → then caching. Cache only what you've measured as hot and expensive.
- Async for slow side-effects: anything the user shouldn't wait for (emails, SMS, PDFs, report generation, webhooks out) moves to a background worker + queue. This is usually the first real architecture step a product needs.
- Scheduled work: cron/scheduler for periodic jobs — make every job idempotent and overlap-safe (lock or skip if previous run alive).
- Horizontal app scaling: stateless app servers behind a load balancer. Requires: no local file writes (object storage), no in-memory sessions (token/DB), no in-process cron duplication.
- Database scaling: connection pooling → read replicas (accepting replica lag on reads that tolerate it) → partitioning by time/tenant. Sharding is the last resort, not a flex.
Caching — the rules that keep it from lying
- Every cache answers three questions in writing: what is the source of truth? how does invalidation happen? what is the maximum acceptable staleness? "TTL 60s" is a fine answer; "we'll invalidate carefully" is not.
- Cache aside (read-through) is the default pattern. Never cache anything permission-scoped under a key that lacks the principal/tenant — cache poisoning across tenants is a breach, not a bug.
- Clear or version caches on auth changes (login/logout) — stale cross-account data is the classic SPA bug.
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 · 60 lines · 84 tokens per session scan A c5195d15462b
system-design is a skill published in the GitHub repository 05-deepak-patidar/claude-skills (4 stars, last pushed 3mo ago), licensed MIT. It adds 84 tokens to every session and 1,159 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 2026-08-31.
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