DiagramPreview

DiagramPreview fills a real gap: it's a single browser tab that speaks Mermaid, PlantUML, Graphviz, D2, and draw.io, plus AI generation. You don't install anything, and you don't sign up to preview or convert. That's its superpower — speed. For a full-stack developer writing API docs or a DevOps engineer diagramming a pipeline, it's faster than spinning up a local renderer. The AI generators (Mermaid, PlantUML, draw.io, architecture) are good for drafts. Feeding it a short prompt like 'login flow with JWT' produces a usable sequence diagram about 80% of the time. The Mermaid AI Fixer is genuinely useful — it catches syntax errors and suggests fixes, which saves annoyance. The API debugging workflow (OpenAPI/Postman/HAR to sequence) is a standout: paste a spec, get a diagram. The schema visualizers (JSON Schema, Protobuf, GraphQL, SQL, DBML) are helpful for reviewing contracts before publishing. Where it bites: no offline mode, no real-time collaborative editing, no SSO or team features. It's a solo tool. The free tier is generous but limited — you'll hit the usage cap if you generate many diagrams daily. The Pro plan at $12/mo is reasonable but adds no team features. For a team of five, you're paying $60/mo for five independent accounts with no shared workspaces. Compared to alternatives: Draw.io is free and offers offline mode with Google Drive/OneDrive sync, but lacks AI generation. Mermaid Live Editor is free and open-source but single-format. Lucidchart has team collaboration and SSO but costs more and is heavier. DiagramPreview sits in a nice middle ground: cheap, browser-native, AI-assisted, multi-format. We'd reach for it when documenting an API or generating a quick architecture diagram from rough notes. For polished presentations or team collaboration, we'd