diagram-code

name	diagram-code
description	用于生成或维护 Mermaid、D2、PlantUML 等 code-as-graph 架构图、流程图、时序图、状态图和数据流图；匹配画图、架构图、流程图、sequence、state、graph as code；强调可编辑、可追溯。

Diagram Code

Create or update reviewable graph source code. This skill exists for repository artifacts where format choice, traceability, and parser validation matter.

Core Contract

• Produce Mermaid, D2, PlantUML, DOT, or the repository's existing graph format; do not substitute a raster image unless the user asks for one.
• Reuse the repository's existing diagram language and style when present.
• Map non-obvious nodes and edges to source files, config, documentation, runtime output, or user-provided facts.
• Keep each diagram focused on one operational question and split crowded views.

Diagram Type Gate

Choose the diagram from the question it must answer:

Question	Diagram	Default format
Who uses the system and why?	Use case or context	PlantUML usecase / Mermaid
What parts exist and where are the boundaries?	Architecture / C4	D2
What steps happen in order?	Workflow / flowchart	Mermaid flowchart
Who calls whom during one request?	Sequence	Mermaid or PlantUML sequence
What states can an object enter?	State / lifecycle	Mermaid or PlantUML state
Where does data move and transform?	Data flow / lineage	D2
What runs where?	Deployment / infrastructure	D2

Prefer Mermaid for Markdown workflows and sequences, D2 for architecture and deployment boundaries, and PlantUML when the repository already uses it.

Workflow

1. Read the relevant source paths, existing diagrams, runtime evidence, or user-provided description.
2. Select the smallest view and graph language that answer the question.
3. Use stable semantic node IDs, short labels, meaningful containers, and edge labels only where protocol, data, event, or condition matters.
4. Put source paths or runtime commands in comments or adjacent traceability notes. Mark assumptions instead of drawing them as confirmed facts.
5. Run the smallest available parser or renderer check, such as d2 fmt, d2 --check, mmdc, plantuml -checkonly, or the repository check command. If none is available, report that syntax was reviewed without rendering.

Maintenance Rules

• Patch existing graphs unless their abstraction is wrong.
• Avoid random IDs, timestamps, unnecessary styling, and layout churn.
• Revise crossing-heavy, ambiguous, or overly dense diagrams before delivery.