Is Diagram Preview free?

Diagram Preview is completely free to use.

Diagram Preview: Preview and convert Mermaid, PlantUML, Markdown, Graphviz, D2, draw.io, mind maps, JSON, YAML and developer diagrams online.

DiagramPreview started as a simple Mermaid preview tool, then gradually became a browser-based workspace for developers, technical writers, architects, and product teams who work with visual scripts and structured files.

Today it supports 70+ tools, including:

Mermaid, PlantUML, Graphviz, D2, draw.io, Markdown previews
AI diagram generation and fixing
JSON/YAML/XML/CSV visualizers
OpenAPI, SQL, Prisma, DBML, GraphQL, Protobuf diagram tools
Docker, Kubernetes, Terraform, GitHub Actions, Nginx, Helm visualizers
Grafana dashboard and Prometheus alert rule generators
SEO/debug tools like robots.txt tester, sitemap viewer, Open Graph preview debugg