RunLocalTools

Free Mermaid Diagram Editor — Live Preview, Export & Save Locally

Create, edit, validate, and export Mermaid diagrams for free. Live preview, SVG and high-resolution PNG, PDF, templates, multiple diagrams, and local autosave — no account required.

What it does

Mermaid Editor is a free browser-based workspace for writing Mermaid diagram syntax and previewing the result as you type. Work with multiple diagrams, start from editable templates, troubleshoot syntax errors, customize supported themes, and export diagrams for documentation, presentations, and project notes.

How it works

Write or import Mermaid source in the editor. The pinned Mermaid renderer runs in your browser and draws the diagram locally. Diagrams and preferences are saved in browser storage so you can return after a refresh. Export formats are generated in the browser. Optional libraries are downloaded only when their features are requested; diagram source is not uploaded to a rendering server.

How to use it

  1. Start with the example, create a blank diagram, or choose a template.
  2. Edit the Mermaid source. The preview updates automatically and displays parser errors when the source cannot be rendered.
  3. Use the theme, direction, curve, and layout controls supported by the renderer.
  4. Import .mmd, .mermaid, .txt, or Markdown files. Markdown files with fenced mermaid blocks can create multiple diagrams.
  5. Export SVG, PNG, JPEG, WebP, PDF, or a ZIP of diagram sources and available previews.
  6. Your workspace autosaves locally. Use Clear saved diagrams when you want to remove this tool’s saved workspace and preferences.

FAQ

Is Mermaid Editor free?

Yes. Editing, templates, local autosave, and supported exports are free. There are no subscriptions, watermarks, account requirements, or artificial diagram-count limits in the tool.

Are my diagrams uploaded to a server?

No. Diagram editing, rendering, imports, exports, and share-link compression happen in your browser. The Mermaid renderer and optional libraries may be downloaded from a CDN, but your diagram source is not sent with those library requests.

Can I use the editor offline?

After the required libraries have been downloaded and cached by the browser, some features may continue to work offline. A first visit or a feature whose library is not cached needs an internet connection. Offline availability depends on browser caching and is not guaranteed.

Which file formats can I import?

You can open .mmd, .mermaid, .txt, and .md files. Markdown files with one or more fenced mermaid blocks can be split into editable diagrams. Plain text is treated as Mermaid source.

Can I export a diagram as an image or PDF?

Yes. The editor offers SVG, PNG, JPEG, WebP, and PDF export. Raster exports depend on browser SVG and canvas support; PDF export may download its PDF library on demand. Very large diagrams can exceed browser canvas limits.

A share link compresses the active diagram into the URL in your browser. It does not upload the diagram, but anyone who receives the complete URL may be able to read its contents. Use a file export instead for sensitive diagrams.

Privacy

Mermaid source, imported files, rendering, browser autosave, image conversion, and share-link compression are processed locally. Saved diagrams and preferences remain in browser storage for this tool until you clear them or the browser removes site data. The Mermaid renderer is lazily downloaded from a pinned CDN. PDF and optional layout libraries may also be downloaded when requested. Those library requests do not include the diagram source. Creating a share link encodes diagram content in the URL; sending or publishing that URL can disclose the diagram to its recipients.

Supported formats

  • Source import: .mmd, .mermaid, .txt, .md (including fenced Mermaid blocks)
  • Diagram export: .svg, .png, .jpg/.jpeg, .webp, .pdf
  • Bulk export: .zip containing Mermaid source files and rendered PNG previews when the browser can render them

Limitations

  • Available syntax and diagram types depend on the pinned Mermaid version and the features supported by that renderer.
  • Some advanced layout options or diagram types may not be available in every Mermaid build.
  • Browser storage can be cleared by the user, browser settings, or storage pressure; export important work as a backup.
  • PNG, JPEG, and WebP export use browser canvas capabilities and are subject to canvas-size limits.
  • PDF export and optional layout engines may require an internet connection the first time they are used.
  • Share links have practical URL-length limits and should not be used for confidential diagrams.