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 The-AI-Directory-Company/agents-and-skills --skill system-design-documentgit clone --depth 1 https://github.com/The-AI-Directory-Company/agents-and-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/the-ai-directory-company/agents-and-skills/system-design-document)<a href="https://agentmods.dev/skills/the-ai-directory-company/agents-and-skills/system-design-document"><img src="https://agentmods.dev/badge/skills/the-ai-directory-company/agents-and-skills/system-design-document/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/the-ai-directory-company/agents-and-skills/system-design-document"><img src="https://agentmods.dev/badge/skills/the-ai-directory-company/agents-and-skills/system-design-document.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 | $0.00032 | $0.01355 |
| Opus 5 | $0.00016 | $0.00678 |
| Sonnet 5 | $0.00006 | $0.00271 |
| Haiku 4.5 | $0.00003 | $0.00136 |
Grade A, and why
system-design-document 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 — 130 lines — stays where its author put it; the contents beside it link to each section on GitHub.
System Design Document
Before you start
Gather the following information. If any is missing, ask the user before proceeding:
- Problem context — What system or feature is being designed? Link to the PRD if one exists.
- Non-functional requirements — Expected load, latency targets, uptime SLA, data retention, compliance needs.
- Constraints — Existing tech stack, team expertise, budget, timeline, vendor commitments.
- Stakeholders — Who reviews this? (e.g., staff engineer, SRE lead, security team)
- Scope boundary — Is this a new system, a major refactor, or an extension of an existing service?
If the user only gives you a vague ask ("design a notification system"), push back: ask about scale (how many notifications/day?), delivery guarantees (at-least-once? exactly-once?), and latency requirements.
System design template
Use the following template. Every section is required unless explicitly marked optional.
Title
[System Name] — System Design Document
1. Context & Motivation (3-5 sentences)
Why does this system need to exist? Reference the PRD or business driver. State what currently exists (if anything) and why it is insufficient.
2. Goals & Non-Goals
Goals — 3-5 specific outcomes this design achieves. Each must be verifiable.
Non-goals — Things this design explicitly does NOT address. This prevents scope creep during review.
3. Non-Functional Requirements
| Requirement | Target | Rationale |
|---|---|---|
| Availability | 99.9% (8.7h downtime/year) | Customer SLA |
| P99 latency | < 200ms | User-facing endpoint |
| Throughput | 5,000 req/s peak | Black Friday projection |
| Data retention | 90 days hot, 2 years cold | Compliance requirement |
4. Architecture Overview
Provide a high-level diagram (Mermaid or ASCII). Show major components, data flow direction, and external dependencies. Label sync vs. async communication. Every box must appear in Section 5.
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.
- 8d ago First seen · 130 lines · 32 tokens per session scan A 14ec843e766c
system-design-document is a skill published in the GitHub repository The-AI-Directory-Company/agents-and-skills (2 stars, last pushed 5mo ago), licensed MIT. It adds 32 tokens to every session and 1,355 once invoked, about $0.0002 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 2026-09-03.
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