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 fattain-naime/engineering-docs --skill database-design-documentgit clone --depth 1 https://github.com/fattain-naime/engineering-docsWrote 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/fattain-naime/engineering-docs/database-design-document)<a href="https://agentmods.dev/skills/fattain-naime/engineering-docs/database-design-document"><img src="https://agentmods.dev/badge/skills/fattain-naime/engineering-docs/database-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/fattain-naime/engineering-docs/database-design-document"><img src="https://agentmods.dev/badge/skills/fattain-naime/engineering-docs/database-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 | $0.00046 | $0.03277 |
| Opus 5.5 | $0.00018 | $0.01311 |
| Sonnet 5.5 | $0.00009 | $0.00655 |
| Haiku 4.5 | $0.00005 | $0.00328 |
Grade A, and why
database-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 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 — 243 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Purpose
Produce a database design document that specifies the complete logical and physical data model, including entity relationships, table definitions, column constraints, indexing strategy, and migration plan.
Database schema is the hardest type of technical debt to remediate. Changing a column name on a 50M-row table is a 4-hour maintenance window. Designing it correctly upfront is a 2-hour design session.
Input
Works best with: The domain or system being modeled. Also valuable: Business rules, cardinality constraints, known query patterns, performance requirements, existing tables that must integrate.
Example invocation: Design the database schema for PayFlow's merchant management system. Merchants have multiple brands, each with their own settings, domains, and staff users. Users have roles with specific permissions. Brands can have multiple currencies and payment methods.
Key Concepts
Normalization
- 1NF: Atomic values. No repeating groups. Single value per cell.
- 2NF: No partial dependencies. Non-key columns depend on the full primary key.
- 3NF: No transitive dependencies. Non-key columns depend only on the primary key.
- BCNF: Stronger form of 3NF. Every determinant is a candidate key.
- Practical rule: Design to 3NF minimum. Denormalize intentionally and explicitly for performance, with documentation.
Indexing Principles
- Every foreign key column must have an index.
- Columns used in
WHERE,JOIN ON, andORDER BYclauses of hot queries must be indexed. - Composite indexes: column order matters. Most selective column first.
- Never index columns with very low cardinality (e.g., a boolean flag) unless combined with a high-cardinality column.
- Generated stored columns for computed or JSON-extracted values that are queried frequently.
Data Integrity
- Use foreign key constraints for referential integrity - do not enforce at application layer only.
- Use CHECK constraints for value validation where supported.
- Use NOT NULL aggressively. NULL means "unknown" - if a value should always be present, make it NOT NULL.
- Use appropriate data types.
DECIMAL(10,2)notFLOATfor money.DATETIME(6)for timestamps.VARCHAR(255)with deliberate limits, not arbitrary.
What ships with it
1 file 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.
- 1mo ago First seen · 243 lines · 46 tokens per session scan A 1fb82d4a04f8
database-design-document is a skill published in the GitHub repository fattain-naime/engineering-docs (6 stars, last pushed 23d ago), licensed MIT. It adds 46 tokens to every session and 3,277 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 2026-08-31.
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