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 cosmicstack-labs/mercury-agent-skills --skill database-designgit clone --depth 1 https://github.com/cosmicstack-labs/mercury-agent-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/cosmicstack-labs/mercury-agent-skills/database-design)<a href="https://agentmods.dev/skills/cosmicstack-labs/mercury-agent-skills/database-design"><img src="https://agentmods.dev/badge/skills/cosmicstack-labs/mercury-agent-skills/database-design.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 | $0.00020 | $0.00443 |
| Opus 5 | $0.00010 | $0.00221 |
| Sonnet 5 | $0.00004 | $0.00089 |
| Haiku 4.5 | $0.00002 | $0.00044 |
Grade A, and why
database-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 7d 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.
What it actually says
Database Design
Design efficient, scalable database schemas.
Normalization
| Normal Form | Rule | Violation Example |
|---|---|---|
| 1NF | Atomic columns, no repeating groups | phone_numbers: "555-0100,555-0200" |
| 2NF | 1NF + all non-key cols depend on full PK | Orders table with product details |
| 3NF | 2NF + no transitive dependencies | Employee with department_name (dept info in dept table) |
When to denormalize: Read-heavy workloads, reporting, caching layers.
Indexing Strategy
Index Types
| Index | Use Case | Tradeoff |
|---|---|---|
| B-Tree | General purpose, equality + range | Default, usually best |
| Hash | Equality only | Fast lookups, no sorting |
| GIN | Array/JSON | Slightly slower writes |
| BRIN | Huge sorted tables | Very small size |
Rules
- Index columns used in WHERE, JOIN, ORDER BY
- Index foreign keys
- Covering indexes for frequent queries
- Don't over-index (slows writes, uses space)
- Drop unused indexes (use pg_stat_user_indexes)
Migrations
- One file per change, sequential naming
- Always reversible (up/down pair)
- Test on staging before production
- Run in transactions where possible
- Avoid locking tables on large tables (use pt-online-schema-change)
Query Optimization
- EXPLAIN ANALYZE every slow query
- Look for: Seq scans, nested loops, temp files
- Common fixes: missing index, bad join order, OR conditions
- N+1 problem: batch find / includes / joins
- Limit offsets for pagination (use cursor-based)
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.
- 7d ago First seen · 55 lines · 20 tokens per session scan A 673a6482dc90
database-design is a skill published in the GitHub repository cosmicstack-labs/mercury-agent-skills (471 stars, last pushed 12d ago), licensed MIT. It adds 20 tokens to every session and 443 once invoked, about $0.0001 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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