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