# Gen Uml

> Use when you need a Mermaid diagram (architecture, flow, or sequence) generated from existing code, and a check that the diagram matches what was actually built.

- Skill: `endika/gen-uml` (Agent Skill)
- Install (CLI): `npx skillmds@latest add endika/gen-uml`
- Raw SKILL.md: https://api.skillmd.com/api/skills/endika/gen-uml/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: Endika (https://skillmd.com/u/endika)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/endika/gen-uml

---


# gen-uml

## Overview

Generate a **Mermaid** diagram from existing code — architecture, flow, or sequence — and
verify it reflects what the code actually does, not what it was supposed to do.

## Steps

1. **Read the real code** for the slice you're diagramming (entry points, modules,
   call/data flow). Diagram what exists.
2. **Pick the diagram type** that answers the question being asked (below).
3. **Emit Mermaid.**
4. **Match-check (required):** walk the diagram against the code one node/edge at a time.
   Every box maps to a real module/function; every arrow to a real call/dependency. Drop or
   fix anything you can't point to in the source. A diagram that quietly diverges is worse
   than none.

## Types & examples

**Architecture** (modules/dependencies):

```mermaid
graph TD
  UI[UI] --> UC[Use cases]
  UC --> SVC[Services]
  SVC --> REPO[Repository]
  REPO --> DB[(Store)]
```

**Flow** (a process / decision path):

```mermaid
flowchart TD
  A[Receive task] --> B{Brownfield?}
  B -- yes --> C[Explore code]
  B -- no --> D[Brainstorm]
  C --> D --> E[Plan]
```

**Sequence** (interaction over time):

```mermaid
sequenceDiagram
  participant C as Client
  participant R as Repo
  participant DB as Store
  C->>R: save(entity)
  R->>DB: update(blob)
  DB-->>R: version
  R-->>C: ok
```

## Output

The Mermaid block plus one line per diagram confirming the match-check passed (or listing
what was corrected).