About Mermaid Online

Writing Mermaid is solved: the syntax is simple and renderers are everywhere. What was unsolved was the step after — turning code into an image you can actually publish. The default output tends to be a low-resolution screenshot with cramped spacing, and most tools in this category either stamp a watermark on the free tier or gate basic export quality behind an account.

So the product is built around one promise: the editor and the export are genuinely free — PNG, JPG, WebP, SVG, and PDF, up to 4x scale, transparent backgrounds, no watermark, no signup. Your diagram code is rendered in your browser and never uploaded by the editor. Exports you download are yours to use anywhere, commercial work included — no separate license needed.

The core workflow — editing, preview, and image export — runs entirely in your browser. Mermaid code you type or paste is not sent to this site’s servers. Autosave lives in your own browser storage.

The optional AI features (generate, repair, refine, image-to-Mermaid) are the exception: using them sends your prompt — or the uploaded image — to a third-party AI provider — Zhipu AI’s GLM-5.3-Flash model — to produce a response. That flow is described in the privacy policy. Everything else never leaves your device.

The editor, the preview, and all standard exports are free, unlimited, and need no account. The optional AI features include 10 free credits after a Google sign-in. Beyond that, a Pro subscription and one-off credit packs keep the servers and the AI usage paid for — and the free tier stays free.

Mermaid Online is built by the developer behind BG Remover Online, which removes the background from images and short videos and returns files with a real alpha channel, and EditableImage, which turns a screenshot of a slide, diagram, or poster back into an editable file.

Questions, bug reports, or feature requests: hello@mermaidonline.org. Feedback from real diagrams that misbehave is especially welcome — include the Mermaid code if you can.