Mermaid Studio

Expert-level Mermaid diagram creation, validation, and multi-format rendering. Creates diagrams from descriptions or code analysis, validates syntax, and renders to SVG, PNG, or ASCII with professional theming.

Golden Rules — Elegant Diagrams by Default

Every diagram MUST follow these principles. They are not optional — they define the difference between a mediocre diagram and a gold-standard one.

Rule 1: Always Use an Init Directive for Professional Styling

NEVER create a diagram without an %%{init} directive or frontmatter config. The default Mermaid theme produces harsh black lines and generic colors. Always apply a curated palette.

For general diagrams (flowchart, sequence, state, class, ERD):

%%{init: {'theme': 'base', 'themeVariables': { 'primaryColor': '#4f46e5', 'primaryTextColor': '#ffffff', 'primaryBorderColor': '#3730a3', 'lineColor': '#94a3b8', 'secondaryColor': '#10b981', 'tertiaryColor': '#f59e0b', 'background': '#ffffff', 'mainBkg': '#f8fafc', 'nodeBorder': '#cbd5e1', 'clusterBkg': '#f1f5f9', 'clusterBorder': '#e2e8f0', 'titleColor': '#1e293b', 'edgeLabelBackground': '#ffffff', 'textColor': '#334155' }}}%%

⚠️ Font Warning: Do NOT set fontFamily in theme variables. The Mermaid default font (trebuchet ms, verdana, arial, sans-serif ) works everywhere. Setting system-ui , Segoe UI , or -apple-system will render as Times New Roman in headless Chromium (used by mmdc ).

For C4 diagrams — see the dedicated C4 styling section below.

For architecture-beta diagrams — see the dedicated AWS/Architecture section below.

Rule 2: Soft Lines, Never Harsh Black

The single biggest visual improvement is using lineColor: '#94a3b8' (slate-400) instead of the default black. This creates a modern, breathable diagram. For dark themes, use lineColor: '#64748b' (slate-500).

Rule 3: Limit Density — Breathe

• Maximum 15 nodes per diagram (not 20 — fewer is more elegant)

• Use subgraph or boundaries to create whitespace and visual grouping

• Prefer LR (left-right) for process flows — it reads more naturally

• Use invisible links (A ~~~ B ) to add spacing when the layout is cramped

Rule 4: Meaningful Labels and Consistent Style

• Node IDs: camelCase (orderService , not s1 or os )

• Labels: short, clear natural language ([Order Service] )

• Arrows: action verbs with protocol info ("Sends order via gRPC" )

• Descriptions: one-line, role-focused ("Handles order lifecycle" )

Rule 5: Color Harmony Over Color Variety

Use max 3-4 colors per diagram. Map colors to meaning:

• Blue tones (#4f46e5, #3b82f6) → primary systems, internal services

• Green tones (#10b981, #059669) → success states, data stores

• Amber tones (#f59e0b, #d97706) → external systems, warnings

• Slate tones (#64748b, #94a3b8) → lines, borders, secondary elements

• Red tones (#ef4444) → errors ONLY, never as decoration

Modes of Operation

This skill operates in three modes based on user intent:

Mode Trigger What happens

Create "draw a diagram of...", "visualize my..." Generates .mmd code only

Render "render this mermaid", "convert to SVG/PNG/ASCII" Renders existing .mmd

Full "create and render...", ambiguous requests Create → Validate → Render

Default to Full mode when intent is unclear.

Step 1: Understand the Request

Before writing any Mermaid code, determine:

• What to diagram — system, flow, schema, architecture, code structure?

• Which diagram type — use the Decision Matrix below

• Output format — code only, SVG, PNG, or ASCII?

• Theme preference — ask only if rendering; default to base theme with curated palette

Diagram Type Decision Matrix

User describes... Diagram Type Syntax keyword

Process, algorithm, decision tree, workflow Flowchart flowchart TD/LR

API calls, message passing, request/response Sequence sequenceDiagram

Database schema, table relationships ERD erDiagram

OOP classes, domain model, interfaces Class classDiagram

State machine, lifecycle, transitions State stateDiagram-v2

High-level system overview (C4 Level 1) C4 Context C4Context

Applications, databases, services (C4 Level 2) C4 Container C4Container

Internal components (C4 Level 3) C4 Component C4Component

Request flows with numbered steps C4 Dynamic C4Dynamic

Infrastructure, cloud deployment C4 Deployment C4Deployment

Cloud services with icons (AWS/GCP/Azure) Architecture architecture-beta

Project timeline, scheduling Gantt gantt

Proportional data, percentages Pie pie

Brainstorming, hierarchical ideas Mindmap mindmap

Historical events, chronology Timeline timeline

Branching strategy, git history Git Graph gitGraph

Flow quantities, resource distribution Sankey sankey-beta

X/Y data visualization XY Chart xychart-beta

Priority matrix, strategic positioning Quadrant quadrantChart

Layout control, grid positioning Block block-beta

Network packets, protocol headers Packet packet-beta

Task boards, kanban workflow Kanban kanban

User experience, satisfaction scoring User Journey journey

System requirements traceability Requirement requirementDiagram

If the user's description doesn't clearly map to one type, suggest 2-3 options with a brief rationale for each, then let them choose.

When to Load References

Load reference files ONLY when needed for the specific diagram type:

• C4 diagrams → Read references/c4-architecture.md BEFORE writing code

• AWS/Cloud architecture → Read references/aws-architecture.md BEFORE writing code

• Code-to-diagram → Read references/code-to-diagram.md BEFORE analyzing

• Theming/styling → Read references/themes.md when user requests custom themes

• Syntax errors → Read references/troubleshooting.md when validation fails

• Any diagram type details → Read references/diagram-types.md for comprehensive syntax

Step 2: Create the Diagram

2.1 — Write Mermaid Code

Follow these principles in order of priority:

• Elegance first — every diagram must look professional with init directives and curated colors

• Correctness — valid syntax that renders without errors

• Clarity — meaningful labels, logical flow direction, clear relationships

• Simplicity — under 15 nodes per diagram; split complex systems into multiple

• Consistency — uniform naming (camelCase for IDs, descriptive labels in brackets)

2.2 — Structure Rules

%% Diagram: [Purpose] | Author: [auto] | Date: [auto] %%{init: {'theme': 'base', 'themeVariables': { ... }}}%% [diagramType] [content]

CRITICAL: The %%{init} directive MUST go on the very first non-comment line, BEFORE the diagram type declaration. Alternatively, use YAML frontmatter at the absolute start of the file.

Naming conventions:

• Node IDs: camelCase, descriptive (orderService , not s1 )

• Labels: natural language in brackets ([Order Service] )

• Relationships: action verbs ("Sends order to" , "Reads from" )

Layout best practices:

• TD (top-down) for hierarchical flows and processes

• LR (left-right) for timelines, pipelines, and sequential processes

• RL for right-to-left reading contexts

• Use subgraph to group related nodes; name subgraphs meaningfully

• Add direction inside subgraphs when needed for different flow

2.3 — Quick Reference Examples

Flowchart (with professional styling):

%%{init: {'theme': 'base', 'themeVariables': { 'primaryColor': '#4f46e5', 'primaryTextColor': '#fff', 'primaryBorderColor': '#3730a3', 'lineColor': '#94a3b8', 'secondaryColor': '#10b981', 'tertiaryColor': '#f59e0b', 'background': '#ffffff', 'mainBkg': '#f8fafc', 'nodeBorder': '#cbd5e1', 'clusterBkg': '#f1f5f9', 'clusterBorder': '#e2e8f0', 'titleColor': '#1e293b', 'edgeLabelBackground': '#ffffff' }}}%% flowchart TD Start([Start]) --> Input[/User Input/] Input --> Validate{Valid?} Validate -->|Yes| Process[Process Data] Validate -->|No| Error[Show Error] Error --> Input Process --> Save[(Save to DB)] Save --> End([End])

For sequence diagram and ERD styling examples, read references/themes.md .

C4 Context (with MANDATORY elegant styling):

C4Context title System Context — E-Commerce Platform

Person(customer, "Customer", "Places orders online")
System(platform, "E-Commerce Platform", "Handles orders and payments")
System_Ext(payment, "Payment Gateway", "Processes transactions")
System_Ext(email, "Email Service", "Sends notifications")

Rel(customer, platform, "Uses", "HTTPS")
Rel(platform, payment, "Processes payments", "API")
Rel(platform, email, "Sends emails", "SMTP")

UpdateRelStyle(customer, platform, $textColor="#475569", $lineColor="#94a3b8")
UpdateRelStyle(platform, payment, $textColor="#475569", $lineColor="#94a3b8")
UpdateRelStyle(platform, email, $textColor="#475569", $lineColor="#94a3b8")

UpdateLayoutConfig($c4ShapeInRow="3", $c4BoundaryInRow="1")

Architecture (AWS with Iconify icons):

architecture-beta group vpc(logos:aws-vpc)[VPC]

service api(logos:aws-api-gateway)[API Gateway] in vpc
service lambda(logos:aws-lambda)[Lambda] in vpc
service db(logos:aws-dynamodb)[DynamoDB] in vpc
service s3(logos:aws-s3)[S3 Bucket]

api:R --> L:lambda
lambda:R --> L:db
lambda:B --> T:s3

IMPORTANT: Architecture-beta diagrams with logos:* icons require icon pack registration. When rendering with the render script, use the --icons logos flag. If rendering in a markdown viewer that doesn't support icon packs, use the built-in icons (cloud , database , disk , server , internet ) as fallback. Read references/aws-architecture.md for the complete icon catalog and rendering instructions.

For comprehensive syntax of ALL diagram types, read references/diagram-types.md .

C4 Diagrams — Mandatory Styling Guide

C4 diagrams have fixed element styling (blue boxes for systems, gray for persons, etc.), but their relationship lines default to harsh black which creates visual noise. You MUST apply these styling rules:

The C4 Styling Pattern

Every C4 diagram MUST include these directives at the end:

%% === MANDATORY STYLING ===
%% Apply soft line colors to ALL relationships
UpdateRelStyle(fromAlias, toAlias, $textColor="#475569", $lineColor="#94a3b8")
%% Repeat for each Rel() in the diagram

%% Optimize layout spacing
UpdateLayoutConfig($c4ShapeInRow="3", $c4BoundaryInRow="1")

C4 Color Values Reference

Purpose Color Hex Notes

Soft line color Slate-400 #94a3b8

Replaces harsh default black

Line text color Slate-600 #475569

Readable but not dominant

Accent line Blue-400 #60a5fa

For highlighted or primary relationships

Warning line Amber-500 #f59e0b

For external/risky connections

Custom element bg Emerald #10b981

For data stores or success highlights

Custom element bg Indigo #4f46e5

For primary system emphasis

C4 Layout Tips

CRITICAL — Maximum 6 Rel() per diagram. More than 6 relationships causes Dagre to route arrows through nodes, creating unreadable spaghetti. If your system needs more connections, split it into multiple focused diagrams.

• Use $c4ShapeInRow="3" for most diagrams (prevents horizontal crowding)

• Use $c4ShapeInRow="2" for diagrams with long labels

• Use $c4BoundaryInRow="1" always (stacks boundaries vertically for clarity)

• Apply $offsetY="-10" to UpdateRelStyle when labels overlap with elements

• Prefer tree-shaped topologies (1 in, 1-2 out per node) over mesh topologies

• Declare elements in flow order — the order of Container() declarations affects layout

• Use directional Rel_D , Rel_R , etc. only as a last resort when auto-layout creates overlapping

For comprehensive C4 syntax, examples, and patterns, read references/c4-architecture.md .

Step 3: Validate

Before rendering, ALWAYS validate the Mermaid syntax:

node $SKILL_DIR/scripts/validate.mjs <file.mmd>

If validation fails:

• Read the error message carefully

• Consult references/troubleshooting.md for common fixes

• Fix the syntax and re-validate

• Maximum 3 fix attempts before asking the user for clarification

Step 4: Render

4.1 — Setup (First Run Only)

bash $SKILL_DIR/scripts/setup.sh

This auto-installs both rendering engines and icon pack dependencies. Run once per environment.

4.2 — Single Diagram Rendering

SVG (default — best quality)

node $SKILL_DIR/scripts/render.mjs -i diagram.mmd -o diagram.svg

PNG (for documents/presentations)

node $SKILL_DIR/scripts/render.mjs -i diagram.mmd -o diagram.png --width 1200

ASCII (for terminals/READMEs)

node $SKILL_DIR/scripts/render-ascii.mjs -i diagram.mmd

With icon packs (architecture-beta with AWS/tech icons)

node $SKILL_DIR/scripts/render.mjs -i diagram.mmd -o diagram.svg --icons logos,fa

The --icons flag registers Iconify packs before rendering. Packs: logos (AWS/tech), fa (Font Awesome). Use logos for AWS.

4.3 — Batch Rendering

For multiple diagrams at once:

node $SKILL_DIR/scripts/batch.mjs
--input-dir ./diagrams
--output-dir ./rendered
--format svg
--theme default
--workers 4

4.4 — Available Themes

beautiful-mermaid (15): tokyo-night | tokyo-night-storm | tokyo-night-light | dracula | nord | nord-light | catppuccin-mocha | catppuccin-latte | github-dark | github-light | solarized-dark | solarized-light | one-dark | zinc-dark | zinc-light

mermaid-cli native (5): default | forest | dark | neutral | base

Custom theme: --theme base --config '{"theme":"base","themeVariables":{"primaryColor":"#4f46e5","lineColor":"#94a3b8"}}'

For the full theme catalog, read references/themes.md . The render script auto-selects the best engine (mmdc primary, beautiful-mermaid fallback, Puppeteer for icon packs).

Step 5: Code-to-Diagram (When Requested)

When the user asks to visualize existing code or architecture:

• Read references/code-to-diagram.md for the analysis methodology

• Analyze the codebase to identify the right diagram type:

• Module dependencies → Flowchart or Class diagram

• API routes and handlers → Sequence diagram

• Database models/schemas → ERD

• Service architecture → C4 Container or Architecture diagram

• State machines in code → State diagram

• Generate the .mmd file with proper init directives (Golden Rule 1)

• Validate and render as usual

Troubleshooting Quick Reference

Symptom Likely Cause Fix

Diagram won't render Syntax error Run validate.mjs, check brackets/quotes

Labels cut off Text too long Shorten labels or use line breaks <br/>

Layout looks wrong Wrong direction Try different TD/LR/BT/RL

Nodes overlap Too many nodes Split into subgraphs or multiple diagrams

Lines too dark/thick No init directive Add %%{init} with lineColor: '#94a3b8'

C4 lines overlapping No styling applied Add UpdateRelStyle with offsets to each Rel

AWS icons not showing No icon pack Use --icons logos flag or fallback to built-in icons

mmdc not found Not installed Run setup.sh

Theme not applied Wrong engine beautiful-mermaid themes only work with that engine

For comprehensive troubleshooting, read references/troubleshooting.md .

Output Conventions

• Save .mmd source files alongside rendered outputs

• Naming: {purpose}-{type}.mmd (e.g., auth-flow-sequence.mmd )

• For batch: maintain input filename, change extension

• Always provide both the .mmd source and rendered file to the user