mermaid

A tool for writing diagrams as Mermaid text, a simple diagram language supported by platforms such as GitHub, GitLab, and documentation tools.

In plain words
What is it for?
Use it for flowcharts, sequence diagrams, class diagrams, state diagrams, timelines, and other supported diagrams in documentation or Markdown.
Why use it?
It makes diagrams easy to generate, store in version control, and edit as text instead of using a drawing application.

Skill for Claude CodeCodex

Part of the diagrams plugin — 6 skills shipped together

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/zate/cc-plugins/mermaid
Any agent
npx skills add Zate/cc-plugins --skill mermaid
Clone the repo
git clone --depth 1 https://github.com/Zate/cc-plugins

Made for: Claude Code, Codex.

Or install diagrams, the plugin that ships this one along with the rest of its 6 skills.

Per session 62 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,685 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 $0.00062 $0.01685
Opus 5 $0.00031 $0.00843
Sonnet 5 $0.00012 $0.00337
Haiku 4.5 $0.00006 $0.00169

Measured 3d ago against content hash 5b4a304108d7, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mermaid 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 3d 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.

plugins/diagrams/skills/mermaid/SKILL.md · 220 lines

How it starts

The opening of the file, as written. The whole thing — 220 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Mermaid Diagram Skill

Generate diagrams using Mermaid's Markdown-inspired syntax. Mermaid is the most token-efficient and LLM-reliable diagram format, with native rendering in GitHub, GitLab, Obsidian, Notion, and many documentation platforms.

When to use Mermaid:

  • User explicitly asks for Mermaid format
  • User wants inline-editable text diagrams in version control
  • User wants to convert an existing SVG/diagram to a simpler text format
  • Mermaid-specific types like Gantt, Sankey, or git graphs

When another format is better:

  • Maximum visual quality and custom design (SVG)
  • Informal whiteboard/sketch aesthetic (Excalidraw)
  • Threat models, comparisons, Venn diagrams (SVG -- Mermaid lacks these types)
  • Complex architecture with nested containers (D2)

Consult the design-system skill for color, composition, and quality rules.

Supported Diagram Types

Type Syntax Keyword Best For
Flowchart flowchart TD or flowchart LR Process flows, decision trees, pipelines
Sequence sequenceDiagram API calls, request lifecycles, protocols
Class classDiagram OOP design, domain models
State stateDiagram-v2 Object lifecycles, state machines
ER Diagram erDiagram Database schemas, data models
Gantt gantt Project timelines, schedules
Mind Map mindmap Topic hierarchies, brainstorming
Timeline timeline Chronological events
Sankey sankey-beta Volume/flow distribution
Pie pie Simple proportions
Git Graph gitGraph Branch/merge visualization
C4 Context C4Context System context diagrams

Syntax Quick Reference

Flowchart

flowchart TD
    A[Start] --> B{Decision?}
    B -->|Yes| C[Action A]
    B -->|No| D[Action B]
    C --> E[End]
    D --> E

Direction: TD (top-down), LR (left-right), BT (bottom-top), RL (right-left).

Node shapes:

  • [text] -- rectangle
  • (text) -- rounded rectangle
  • {text} -- diamond (decision)
  • ([text]) -- stadium/pill
  • [[text]] -- subroutine
  • [(text)] -- cylinder (database)
  • ((text)) -- circle

Read the full file on GitHub · 220 lines

Files

What ships with it

4 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.

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. 3d ago First seen · 220 lines · 62 tokens per session scan A 5b4a304108d7

Subscribe to this mod's changes

mermaid is a skill published in the GitHub repository Zate/cc-plugins (10 stars, last pushed 1mo ago), licensed MIT. It adds 62 tokens to every session and 1,685 once invoked, about $0.0003 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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