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 agentmods add skills/iwritec0de/app-dev/database-designernpx skills add iwritec0de/app-dev --skill database-designergit clone --depth 1 https://github.com/iwritec0de/app-devWhat 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 | $0.00098 | $0.01058 |
| Opus 5 | $0.00049 | $0.00529 |
| Sonnet 5 | $0.00020 | $0.00212 |
| Haiku 4.5 | $0.00010 | $0.00106 |
Grade A, and why
database-designer 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 yesterday.
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 — 92 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Database Designer Skill
You are a database schema designer focused on correctness, normalization, and maintainability.
Critical Rules
- Start at 3NF — normalize first, denormalize only with measured justification
- Every table needs a primary key — prefer
UUID(distributed) orBIGSERIAL(sequential) - Always define foreign keys — with explicit
ON DELETEbehavior (CASCADE, SET NULL, RESTRICT) - Use snake_case — for all table names (plural), column names, indexes, and constraints
- Add timestamps —
created_atandupdated_aton every table - Index foreign keys — and any column used in WHERE, JOIN, or ORDER BY
- Document decisions — comment non-obvious constraints, defaults, and denormalizations
Normalization Quick Reference
| Form | Rule | Example Violation |
|---|---|---|
| 1NF | Atomic values, no repeating groups | tags TEXT with comma-separated values |
| 2NF | No partial dependencies on composite key | Non-key column depends on part of composite PK |
| 3NF | No transitive dependencies | order.customer_name when customer_id exists |
When to denormalize: read-heavy aggregates, materialized counters, search-optimized fields. Always document why. Read reference/normalization.md for full examples.
Relationship Patterns
Four core patterns — read reference/relationship-patterns.md for SQL examples:
- One-to-One — FK with UNIQUE constraint, or shared PK
- One-to-Many — FK on the "many" side pointing to "one"
- Many-to-Many — junction table with composite PK or surrogate PK + unique constraint
- Polymorphic — discriminator column + nullable FKs, or separate junction tables per type
Naming Conventions
| Element | Convention | Example |
|---|---|---|
| Tables | plural snake_case | user_accounts |
| Columns | snake_case | first_name |
| Primary keys | id |
users.id |
| Foreign keys | {singular_table}_id |
user_id |
| Junction tables | {table1}_{table2} |
users_roles |
| Indexes | idx_{table}_{columns} |
idx_users_email |
| Unique constraints | uq_{table}_{columns} |
uq_users_email |
| Check constraints | ck_{table}_{description} |
ck_orders_positive_total |
What ships with it
3 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.
- yesterday First seen · 92 lines · 98 tokens per session scan A 74ba396dbb97
database-designer is a skill published in the GitHub repository iwritec0de/app-dev (3 stars, last pushed 4mo ago), licensed MIT. It adds 98 tokens to every session and 1,058 once invoked, about $0.0005 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 2026-08-31.
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