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 kok-o/contextos-agents --skill system-designgit clone --depth 1 https://github.com/kok-o/contextos-agentsWrote 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/kok-o/contextos-agents/system-design)<a href="https://agentmods.dev/skills/kok-o/contextos-agents/system-design"><img src="https://agentmods.dev/badge/skills/kok-o/contextos-agents/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/kok-o/contextos-agents/system-design"><img src="https://agentmods.dev/badge/skills/kok-o/contextos-agents/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 | $0.00061 | $0.03429 |
| Opus 5.5 | $0.00024 | $0.01372 |
| Sonnet 5.5 | $0.00012 | $0.00686 |
| Haiku 4.5 | $0.00006 | $0.00343 |
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 today.
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.
Copies of this mod
1 near-identical copy found in the catalogue:
- system-design — 89% identical, 40 lines differ
How it starts
The opening of the file, as written. The whole thing — 420 lines — stays where its author put it; the contents beside it link to each section on GitHub.
system-design
Overview
Scalable system architecture blueprint based on the System Design Primer and DDIA. Enforces load balancing, multi-tier caching (Redis, CDN), database partitioning, CAP theorem tradeoffs, and rate limiting before code is written.
When to Use
Activate during the PLAN phase of any backend service, API design, database schema creation, or scalability optimization.
Rules & Patterns
Based on donnemartin/system-design-primer - the most starred system design resource on GitHub.
Core Principle
Everything is a trade-off. Before writing a single line of backend code, reason through the system at scale. A flat monolith that works now fails at 10× load.
Mandatory Pre-Design Checklist
Before architecting any backend system, answer these questions:
- Scale: What is the expected QPS (queries per second)? Peak vs average?
- Data volume: How much data? Growth rate? 1GB? 1TB? 1PB?
- Consistency vs Availability: Can we tolerate eventual consistency? (CAP theorem)
- Read/Write ratio: Is it read-heavy (cache it!) or write-heavy (shard it!)?
- Latency requirements: Real-time (<100ms)? Near-real-time (<1s)? Batch?
- Global distribution: Single region or multi-region?
- Deployment model: Traditional servers, Serverless, or Edge functions?
Core Architecture Patterns
Load Balancing
Clients → Load Balancer → [App Server 1, App Server 2, App Server N]
- Use Round Robin for stateless services
- Use Least Connections for varying request times
- Use IP Hash for session affinity (or move sessions to Redis)
- Always add health checks - remove unhealthy nodes automatically
Rule: Any service expecting > 1000 RPS needs a load balancer. No exceptions.
Caching Strategy
App → [Cache Layer: Redis/Memcached] → Database
Cache decision ladder (check in order):
- Is it read > write? → Cache it
- Is it expensive to compute? → Cache it
- Is it user-specific? → Cache with user key
- Is it global? → Shared cache, shorter TTL
What ships with it
4 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.
- today First seen · 420 lines · 61 tokens per session scan A 97cfd123b4ce
system-design is a skill published in the GitHub repository kok-o/contextos-agents (10 stars, last pushed today), licensed Apache-2.0. It adds 61 tokens to every session and 3,429 once invoked, about $0.0002 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 2026-10-25.
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