A coding skill for generating Mermaid diagrams in files or Markdown code blocks. Mermaid is a text-based format that turns structured descriptions into diagrams.

Use it to create flowcharts, sequence, class, database-relationship, state, Gantt, pie, mind-map, timeline, and Git-history diagrams.

It lets developers keep diagrams alongside documentation and update them by editing text.

mermaid — Skill for Claude Code and Codex by johnlarkin1: A coding skill for generating Mermaid diagrams in files…

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/johnlarkin1/claude-code-extensions/mermaid

Any agent

npx skills add johnlarkin1/claude-code-extensions --skill mermaid

Clone the repo

git clone --depth 1 https://github.com/johnlarkin1/claude-code-extensions

Made for: Claude Code, Codex.

Or install diagram-code, the plugin that ships this one along with the rest of its 3 skills, 1 agent.

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/johnlarkin1/claude-code-extensions/mermaid.svg)](https://agentmods.dev/skills/johnlarkin1/claude-code-extensions/mermaid)

Your own site

<a href="https://agentmods.dev/skills/johnlarkin1/claude-code-extensions/mermaid"><img src="https://agentmods.dev/badge/skills/johnlarkin1/claude-code-extensions/mermaid.svg" alt="Measured on agentmods" height="20"></a>

Per session 105 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,357 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin unknown 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	$0.00105	$0.01357
Opus 5	$0.00053	$0.00678
Sonnet 5	$0.00021	$0.00271
Haiku 4.5	$0.00011	$0.00136

Measured 4d ago against content hash 66590f9dd092, 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 4d 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/diagram-code/skills/mermaid/SKILL.md · 222 lines

The source is not reproduced here

No licence file

Read it on GitHub

Files

What ships with it

2 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.

4d ago First seen · 222 lines · 105 tokens per session scan A 66590f9dd092

Subscribe to this mod's changes

mermaid is a skill published in the GitHub repository johnlarkin1/claude-code-extensions (21 stars, last pushed 1mo ago), with no licence file. It adds 105 tokens to every session and 1,357 once invoked, about $0.0005 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.

Git and workflow Writing and docs claude-code claude-plugins

watch

File sentinel that monitors the working directory for changes and marker comments, then auto-triggers appropriate skills. Poll-based via git diff against the last scan commit. Writes intake items for batch processing and routes marker actions through /do. Use for automatic reactions to file changes; do NOT use for…

SethGammon/Citadel · 70 tokens

review

5-pass structured code review — correctness, security, performance, readability, consistency.

SethGammon/Citadel · 17 tokens

live-preview

Mid-build visual verification loop. Takes screenshots of components during construction, not just after. Catches visual regressions and invisible features before they compound. Requires Playwright or similar screenshot tool.

SethGammon/Citadel · 40 tokens

marshal

Meta-orchestrator that takes any direction — broad, specific, or vague — and autonomously chains skills and context into actionable work. Gathers context from codebase, docs, and memory. Only asks the user when it genuinely cannot proceed. Single-session orchestrator.

SethGammon/Citadel · 56 tokens

wiki

Markdown-first knowledge base where the LLM acts as librarian. Ingests raw sources, compiles and interlinks topic files, self-maintains an index. No vector DB or embeddings required -- uses LLM-native navigation over structured markdown up to 400K words.