What is 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.

Use it after migrations change tables, columns, or foreign-key constraints, or whenever the database diagram needs to match the current MySQL schema.

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 This avoids relying on a diagram that has become outdated.

How nerds-odd-e/doughnut configures Claude Code and Codex

Reuse

Borrowing it

Nothing to install: this file belongs to nerds-odd-e/doughnut. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/nerds-odd-e/doughnut/main/.agents/skills/database-erd/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/nerds-odd-e/doughnut

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/nerds-odd-e/doughnut/database-erd/github.svg)](https://agentmods.dev/skills/nerds-odd-e/doughnut/database-erd)

Your own site

<a href="https://agentmods.dev/skills/nerds-odd-e/doughnut/database-erd"><img src="https://agentmods.dev/badge/skills/nerds-odd-e/doughnut/database-erd/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/nerds-odd-e/doughnut/database-erd"><img src="https://agentmods.dev/badge/skills/nerds-odd-e/doughnut/database-erd.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

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. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

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.

Model	Per session	Once invoked
Fable 5.1	$0.00071	$0.00825
Opus 5.5	$0.00028	$0.00330
Sonnet 5.5	$0.00014	$0.00165
Haiku 4.5	$0.00007	$0.00082

Measured 2mo ago against content hash 1a4d0a10aee3, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, 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 2mo 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>

Schema catalog used (auto-selected or DONUT_ERD_SCHEMA override).
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.

2mo 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 (50 stars, last pushed today), licensed MIT. It adds 71 tokens to every session and 825 once invoked, about $0.0003 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 2026-08-30.

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doughnut: Skill for Claude Code