kroki-diagram-api

name	kroki-diagram-api
description	Generate diagrams from text via Kroki's multi-format rendering API
metadata	{"openclaw":{"emoji":"📐","category":"tools","subcategory":"diagram","keywords":["Kroki","diagram generation","text-to-diagram","Graphviz","PlantUML","Mermaid"],"source":"https://kroki.io/"}}

Kroki Diagram API

Overview

Kroki provides a unified HTTP API to render 20+ text-based diagram formats into images (SVG, PNG, PDF). It supports Mermaid, PlantUML, Graphviz, D2, BPMN, and more — all through a single endpoint. Self-hostable or use the free public instance. No authentication required. Ideal for generating research figures, architecture diagrams, and flowcharts programmatically.

API Usage

GET Request (URL-encoded)

# Graphviz DOT diagram
curl "https://kroki.io/graphviz/svg/digraph{A->B->C}" -o diagram.svg

# Mermaid diagram (base64-encoded)
echo "graph TD; A-->B; B-->C;" | base64 | \
  curl "https://kroki.io/mermaid/svg/$(cat -)" -o diagram.svg

POST Request (Recommended)

# PlantUML sequence diagram
curl -X POST "https://kroki.io/plantuml/svg" \
  -H "Content-Type: text/plain" \
  -d '@startuml
Alice -> Bob: Hello
Bob --> Alice: Hi!
@enduml' -o sequence.svg

# Mermaid flowchart
curl -X POST "https://kroki.io/mermaid/svg" \
  -H "Content-Type: text/plain" \
  -d 'graph TD
    A[Data Collection] --> B[Preprocessing]
    B --> C[Model Training]
    C --> D[Evaluation]
    D -->|Good| E[Deploy]
    D -->|Bad| B' -o flowchart.svg

# Graphviz
curl -X POST "https://kroki.io/graphviz/svg" \
  -H "Content-Type: text/plain" \
  -d 'digraph {
    rankdir=LR
    "Raw Data" -> "Feature Extraction" -> "Model" -> "Prediction"
  }' -o pipeline.svg

# D2 diagram
curl -X POST "https://kroki.io/d2/svg" \
  -H "Content-Type: text/plain" \
  -d 'Client -> API: Request
API -> Database: Query
Database -> API: Results
API -> Client: Response' -o d2.svg

URL Format

https://kroki.io/{diagram_type}/{output_format}/{encoded_source}

# Or POST to:
https://kroki.io/{diagram_type}/{output_format}

Supported Diagram Types

Type	Keyword	Best for
Mermaid	mermaid	Flowcharts, sequences, Gantt
PlantUML	plantuml	UML, sequences, class diagrams
Graphviz	graphviz	Network graphs, DAGs
D2	d2	Modern text-to-diagram
Ditaa	ditaa	ASCII art diagrams
BlockDiag	blockdiag	Block diagrams
Nomnoml	nomnoml	UML-like diagrams
WaveDrom	wavedrom	Digital timing diagrams
Vega	vega	Data visualizations
Vega-Lite	vegalite	Simplified data viz
C4 PlantUML	c4plantuml	C4 architecture
BPMN	bpmn	Business processes
Bytefield	bytefield	Protocol/byte diagrams
Excalidraw	excalidraw	Hand-drawn style

Output Formats

Format	Extension	Use case
SVG	/svg	Web, scalable
PNG	/png	Documents, slides
PDF	/pdf	Papers, print
JPEG	/jpeg	Compatibility

Python Usage

import requests
import base64
import zlib


KROKI_URL = "https://kroki.io"


def render_diagram(source: str, diagram_type: str = "mermaid",
                   output_format: str = "svg") -> bytes:
    """Render a text diagram to image via Kroki."""
    resp = requests.post(
        f"{KROKI_URL}/{diagram_type}/{output_format}",
        headers={"Content-Type": "text/plain"},
        data=source,
    )
    resp.raise_for_status()
    return resp.content


def save_diagram(source: str, output_path: str,
                 diagram_type: str = "mermaid",
                 output_format: str = "svg"):
    """Render and save a diagram to file."""
    content = render_diagram(source, diagram_type, output_format)
    with open(output_path, "wb") as f:
        f.write(content)


def render_research_pipeline(steps: list) -> bytes:
    """Create a research pipeline flowchart."""
    nodes = []
    for i, step in enumerate(steps):
        node_id = chr(65 + i)
        nodes.append()
         i > :
            prev_id = ( + i - )
            nodes.append()

    mermaid =  + .join(nodes)
     render_diagram(mermaid, , )



workflow = 

save_diagram(workflow, , )


citation_graph = 
save_diagram(citation_graph, , )


pipeline_svg = render_research_pipeline([
    , , ,
    , , 
])

Self-Hosting

# Run Kroki locally via Docker
docker run -d -p 8000:8000 yuzutech/kroki

# Then use http://localhost:8000 instead of https://kroki.io

References

• Kroki
• Kroki Documentation
• Kroki GitHub