kroki-diagrams

A distributable agent skill for turning architecture ideas, flows, schemas, and dependency maps into clean, versionable diagrams.

What Is Kroki?

Kroki is a diagram rendering service. Instead of drawing boxes manually in a GUI, you write diagrams as text using engines like PlantUML, Mermaid, Graphviz, and ERD syntax, then Kroki renders them to SVG, PNG, PDF, or text output.

That gives you a few big advantages:

diagrams live in your repo as source files
changes are diffable in git
diagrams can be regenerated automatically
you can use the best diagram engine for each use case instead of forcing everything into one tool

This skill packages that workflow for coding agents so they do not just dump raw diagram syntax or pick a random engine. It helps them choose the right diagram type, style it sanely, render it, and optionally make it interactive.

Quick Demo

https://github.com/user-attachments/assets/e22072b9-ae73-4405-b6ad-659f2cefc868

What This Skill Actually Does

From start to finish, the skill:

reads your code, docs, or prompt
decides whether you need a sequence diagram, C4 diagram, graph, ERD, Mermaid flow, or even a plain text tree
chooses the most appropriate engine
applies layout and styling rules to avoid spaghetti diagrams
writes the diagram source file into a sensible repo-local folder
renders the source through Kroki
optionally builds an interactive.html viewer around the SVG
automatically updates an index.html page for the diagram collection

So it is not just “render this diagram.” It is a full diagram production workflow.

Feature Set

Use-case-first diagram selection instead of engine-first guessing
Support for plantuml, c4plantuml, graphviz, mermaid, and erd
Readability rules for layout direction, grouping, spacing, and diagram splitting
Engine-specific style templates so diagrams start from a sane visual baseline
Interactive HTML wrappers for supported SVG outputs
Auto-generated collection index.html pages with list and card views
Repo-friendly output placement like docs/diagrams/<artifact-name>/
Shareable Kroki URLs for generated diagram sources
Cross-agent packaging for Claude Code, Codex, and Pi

Interactive Viewer Features

When you render an interactive wrapper, the generated HTML viewer can provide:

click-to-select node highlighting
connected-node and edge emphasis
directional edge flow when the SVG exposes source and target metadata
neutral current-style edge animation when direction is not reliable
dimming of unrelated nodes without making them disappear
fit-to-view on load
pan and zoom controls
a generated diagram index page for browsing many diagrams

Support is strongest for:

PlantUML
C4-PlantUML
Graphviz

Best-effort support exists for:

Mermaid
ERD

Supported Use Cases

This skill is built for tasks like:

architecture diagrams
request and sequence flows
system context and container diagrams
dependency graphs
orchestration DAGs
schema and data relationship diagrams
planning structures and work breakdowns
repo layout visualizations

Examples:

“diagram our authentication flow”
“show the runtime topology of this service”
“generate a dependency graph for these modules”
“make an ERD from this schema”
“visualize this product workflow”

How It Works In Practice

The packaged skill payload lives at plugins/kroki-diagrams/.

Important pieces:

SKILL.md
The main workflow and decision rules.
render_kroki_diagram.py
Renders diagram source through Kroki, prints a shareable URL, writes metadata, and refreshes index.html.
build_interactive_kroki_html.py
Wraps rendered SVG output in an interactive HTML viewer.
build_diagram_index.py
Builds the collection browser page for a directory of diagram artifacts.
references/
Holds the selection matrix, style templates, layout rules, and support notes the agent reads on demand.

Typical Output Structure

The skill usually writes one folder per diagram artifact:

docs/diagrams/my-diagram/
  source.puml
  rendered.svg
  interactive.html
  .diagram-meta.json

And at the parent level it can maintain:

docs/diagrams/index.html

That index is useful once a repo accumulates a larger diagram library.

Example Render Flow

Normal SVG render:

python3 plugins/kroki-diagrams/scripts/render_kroki_diagram.py \
  --engine plantuml \
  --input /path/to/source.puml \
  --output /path/to/rendered.svg

SVG render plus interactive viewer:

python3 plugins/kroki-diagrams/scripts/render_kroki_diagram.py \
  --engine plantuml \
  --input /path/to/source.puml \
  --output /path/to/rendered.svg \
  --interactive-output /path/to/interactive.html

What you get back:

rendered SVG output
optional interactive HTML
a shareable Kroki URL
per-artifact metadata
an updated collection index.html by default

Bundled Examples

This repo includes a ready-to-open sample set under examples/interactive-playground/.

It includes medium-complex examples across the main supported engines:

PlantUML sequence flow
C4-PlantUML container architecture
Graphviz orchestration DAG
Mermaid operational flowchart
ERD schema diagram

Start with:

To rebuild the sample outputs from source:

cd examples/interactive-playground
./render_all.sh

Why Use This Instead Of Plain Mermaid Everywhere?

Because different diagram jobs want different engines.

PlantUML is strong for sequence and architecture diagrams
C4-PlantUML is better for C4 modeling than generic Mermaid boxes
Graphviz is much better for dense graph layouts
Mermaid is great for simpler flows and broad compatibility
ERD syntax is useful for schema views

This skill handles that selection step so the agent does not force one engine onto every problem.

Install

Claude Code

/plugin marketplace add smoldrago/kroki-diagrams
/plugin install kroki-diagrams@kroki-diagrams-marketplace

OpenAI Codex

git clone --depth 1 https://github.com/smoldrago/kroki-diagrams.git /tmp/kroki-diagrams
cp -r /tmp/kroki-diagrams/plugins/kroki-diagrams ~/.agents/skills/kroki-diagrams
rm -rf /tmp/kroki-diagrams

Invoke with $kroki-diagrams or let Codex trigger it implicitly.

Pi

curl -fsSL https://raw.githubusercontent.com/smoldrago/kroki-diagrams/main/install-pi.sh | bash

Or clone and run:

git clone --depth 1 https://github.com/smoldrago/kroki-diagrams.git
cd kroki-diagrams
./install-pi.sh

Repo Layout

.claude-plugin/
  plugin.json
  marketplace.json
plugins/
  kroki-diagrams/
    .claude-plugin/plugin.json
    SKILL.md
    agents/openai.yaml
    references/
    scripts/
install-pi.sh

Limitations

This repo packages the skill, not a standalone desktop app
Interactivity depends on inline SVG output and engine-emitted metadata
Not every Kroki engine is supported equally
Some diagram problems are better split into multiple diagrams instead of one giant graph

Credits

Kroki for the rendering service that turns text-based diagram source into generated outputs across multiple diagram engines
The PlantUML, C4-PlantUML, Graphviz, Mermaid, and ERD ecosystems that make the underlying diagram formats possible

Roadmap

UI refinement and general "desloppification" of the interactive viewer
Dark mode support
Better edge-case handling for large diagrams and inconsistent SVG structures
UI polishing across the viewer and generated index pages
Product presets for common use cases like architecture, sequence, schema, and planning
Theme packs for different visual directions and documentation contexts

License

MIT