database-erd

A command that regenerates a Mermaid entity-relationship diagram from a MySQL database schema. An ER diagram shows tables, their key columns, and the relationships between them.

In plain words
What is it for?
Use it after migrations change tables, columns, or foreign-key constraints, or whenever the database diagram needs to match the current MySQL schema.
Why use it?
It keeps the documented database structure aligned with Flyway migrations, which are versioned database changes. This avoids relying on a diagram that has become outdated.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/nerds-odd-e/doughnut/database-erd
Any agent
npx skills add nerds-odd-e/doughnut --skill database-erd
Clone the repo
git clone --depth 1 https://github.com/nerds-odd-e/doughnut

Made for: Claude Code, Codex.

Per session 71 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 825 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00071 $0.00825
Opus 5 $0.00036 $0.00413
Sonnet 5 $0.00014 $0.00165
Haiku 4.5 $0.00007 $0.00082

Measured 2d ago against content hash 1a4d0a10aee3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

database-erd 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 2d 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.

.agents/skills/database-erd/SKILL.md · 107 lines

What it actually says

Purpose: Keep the schema diagram accurate after Flyway migrations — never hand-edit the Mermaid block.

Output: Updated docs/database-erd.md + summary ending with ## ERD EXPORTED.

Run when:

  • A new or changed Flyway migration alters tables, columns, or constraints
  • The ERD needs to match the current migrated schema

Git does not use the Nix prefix. All other repo tooling does: CURSOR_DEV=true nix develop -c …

Implementation:

  • Script: scripts/export_database_erd.py
  • Output: docs/database-erd.md
  • Omits flyway_schema_history from the diagram

Overrides (optional):

Variable Default
DONUT_ERD_SCHEMA (auto: development → test → e2e)
DONUT_ERD_MYSQL_HOST 127.0.0.1
DONUT_ERD_MYSQL_PORT 3309
DONUT_ERD_MYSQL_USER doughnut
DONUT_ERD_MYSQL_PASSWORD doughnut
CURSOR_DEV=true nix develop -c python3 scripts/export_database_erd.py

Or:

CURSOR_DEV=true nix develop -c pnpm export:database-erd

<success_criteria>

  • MySQL reachable on 127.0.0.1:3309 with user doughnut
  • At least one migrated schema available (or DONUT_ERD_SCHEMA set)
  • Exporter run with Nix prefix
  • docs/database-erd.md updated and ready to commit
  • Final output includes ## ERD EXPORTED </success_criteria>
  1. Schema catalog used (auto-selected or DONUT_ERD_SCHEMA override).
  2. Whether docs/database-erd.md changed.
## ERD EXPORTED

<out_of_scope>

  • Do not hand-edit the Mermaid block in docs/database-erd.md. </out_of_scope>
Changes

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.

  1. 2d ago First seen · 107 lines · 71 tokens per session scan A 1a4d0a10aee3

Subscribe to this mod's changes

database-erd is a skill published in the GitHub repository nerds-odd-e/doughnut (49 stars, last pushed 3d ago), licensed MIT. It adds 71 tokens to every session and 825 once invoked, about $0.0004 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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