Mermaid Expert
Create Mermaid diagrams for flowcharts, sequences, ERDs, and architectures. Masters syntax for all diagram types and styling. Use PROACTIVELY for visual documentation, system diagrams, or process flows.
- Type
- Subagent
- Repository
- nyldn/claude-octopus
- GitHub stars
- 4.1k
- License
- MIT
- Repo last updated
- Sep 26, 2026
- Source file
- agents/personas/mermaid-expert.md
- Model
- haiku
What Mermaid Expert is
Mermaid Expert is a subagent published in the nyldn/claude-octopus repository on GitHub, which has about 4.1k stars. The repository describes itself as: “Run multiple AI models against the same research, design, or coding task. Surface disagreements before you ship.”
A subagent is a specialist assistant that Claude can hand part of a task to. It is a markdown file whose frontmatter sets a name, a description that tells Claude when to delegate, and optionally the tools and model it may use; the body becomes the subagent's own system prompt.
Because a subagent works in its own context, it keeps the main conversation focused: Claude can send a narrow job, such as a review or a specialised analysis, to Mermaid Expert and get back a compact result.
How to install Mermaid Expert
Claude Code
- Download mermaid-expert.md from the repository.
- Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control.
- Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Claude Cowork
- Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent.
- Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.
Inside the source file
An excerpt from agents/personas/mermaid-expert.md, shared under the repository's MIT license. Read the full file on GitHub.
You are a Mermaid diagram expert specializing in clear, professional visualizations.
Focus Areas
- Flowcharts and decision trees
- Sequence diagrams for APIs/interactions
- Entity Relationship Diagrams (ERD)
- State diagrams and user journeys
- Gantt charts for project timelines
- Architecture and network diagrams
Diagram Types Expertise
graph (flowchart), sequenceDiagram, classDiagram,
stateDiagram-v2, erDiagram, gantt, pie,
gitGraph, journey, quadrantChart, timelineApproach
- Choose the right diagram type for the data
- Keep diagrams readable - avoid overcrowding
- Use consistent styling and colors
- Add meaningful labels and descriptions
- Test rendering before delivery
Output
- Complete Mermaid diagram code
- Rendering instructions/preview
- Alternative diagram options
- Styling customizations
- Accessibility considerations
- Export recommendations
Always provide both basic and styled versions. Include comments explaining complex syntax.
Before you install
- Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
- Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
- Try it in a test project or a copy of your files before pointing it at real work.
- Pin the version you tested, and review changes before updating.
- Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.
FAQ
What is Mermaid Expert?
Mermaid Expert is a subagent for Claude Code and Claude Cowork from the nyldn/claude-octopus repository on GitHub. Create Mermaid diagrams for flowcharts, sequences, ERDs, and architectures. Masters syntax for all diagram types and styling. Use PROACTIVELY for visual documentation, system diagrams, or process flows.
How do I install Mermaid Expert in Claude Code?
Download mermaid-expert.md from the repository. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Can I use Mermaid Expert in Claude Cowork?
Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
Is Mermaid Expert safe to install?
It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.
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