Kroki review: the free, open-source diagrams-as-code API's supported diagram types, self-hosting, integrations, and how it compares to alternatives.
Kroki is a free, open-source API that converts plain-text diagram descriptions into rendered images. Created by Guillaume Grossetie under the yuzutech GitHub organization and first published in April 2019, it is released under the MIT license and has grown through community contributions into a project supporting more than 20 diagram-as-code languages.
Rather than requiring separate tooling for each diagram syntax, Kroki exposes one unified HTTP endpoint that accepts markup in languages like Mermaid, PlantUML, or GraphViz and returns SVG, PNG, PDF, or JPEG output, making it a common building block behind documentation sites and internal developer tools.
Kroki supports GET requests with deflate-compressed, base64-encoded diagram source embedded directly in the URL, ideal for linking live diagrams from Markdown or wiki pages, as well as POST requests for larger diagram text. Its modular architecture runs diagram types that need external engines, such as Excalidraw or Structurizr, as separate companion microservices, which keeps the core service lean while still supporting a wide range of syntaxes.
Because Kroki ships as Docker images, teams can self-host it entirely on their own infrastructure to keep sensitive architecture diagrams private, or use the free public instance at kroki.io for quick, no-install access. Official integrations with tools like Asciidoctor, MkDocs, and Confluence let teams embed diagrams-as-code directly into their existing documentation workflows.
Kroki itself is entirely free, both as the publicly hosted kroki.io API and as a self-hosted Docker deployment, since it is an open-source, MIT-licensed community project rather than a commercial product with pricing tiers.
Teams that want a fully managed, self-hosted-equivalent instance without operating the Docker infrastructure themselves can turn to third-party managed hosting providers, such as Elestio, which offer paid hosting plans for Kroki as one of many open-source tools in their catalog.
Kroki is a free, open-source API that converts plain-text diagram descriptions, written in languages like Mermaid, PlantUML, or GraphViz, into rendered images such as SVG or PNG.
No, you can call the free public API at kroki.io directly, or self-host Kroki with Docker if you need full control over your infrastructure.
Kroki supports more than 20 diagram types, including Mermaid, PlantUML, GraphViz, BPMN, C4, Excalidraw, Ditaa, Vega, Vega-Lite, WaveDrom, and Diagrams.net (draw.io).
Yes, Kroki is completely free and open source under the MIT license, both for the hosted public instance and for self-hosted deployments.
Kroki is maintained under the GitHub organization yuzutech, created by Guillaume Grossetie, and was first published in 2019.
Yes, Kroki has integrations for tools such as Asciidoctor, MkDocs, and Confluence, letting teams embed diagrams-as-code directly in their docs.