Built-in Mermaid renderer doesn't support C4Container diagrams (older Mermaid version bundled)

Support Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Cursor’s built-in Mermaid renderer ships a Mermaid version that predates C4Container support.
C4 diagram types (C4Container, C4Component, etc.) were stabilized in Mermaid v10.x. The
bundled version doesn’t include them.

The bierner.markdown-mermaid extension (which bundles Mermaid 11.x and does render C4
correctly) was recently deprecated because VS Code 1.121 merged native Mermaid support.
However, Cursor’s native renderer doesn’t match that parity yet, so users who uninstalled the
now-deprecated extension lose C4 rendering with no recourse.

Steps to Reproduce

  1. Create a .md file with a C4Container diagram (any standard C4 using C4Container, Boundary,
    Container, ContainerDb, System_Ext, Rel)
  2. Open Markdown preview with Cmd+Shift+V

“Mermaid Syntax Error” banner

Expected Behavior

diagram renders

Screenshots / Screen Recordings

Screen Shot 2026-06-10 at 08.36.07.png
Screen Shot 2026-06-10 at 08.36.07.png1982×498 26.2 KB

Operating System

MacOS

Version Information

Version: 3.7.21
VS Code Extension API: 1.105.1
Commit: 517f696d8ab6c53eb04fbfdaae705cd146bf3460
Date: 2026-06-07T21:46:09.237Z
Layout: editor
Build Type: Stable
Release Track: Default
Electron: 39.8.1
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
xterm.js: 6.1.0-beta.256
OS: Darwin x64 21.6.0

For AI issues: which model did you use?

N/A

Additional Information

Workaround: reinstall bierner.markdown-mermaid and use Markdown: Open Preview from its
command rather than the built-in shortcut. The two renderers conflict when both are present;
the extension’s command bypasses the built-in.

Ask: update the bundled Mermaid version to 11.x (or current stable) to match VS Code 1.121’s
native support level.

Does this stop you from using Cursor

No - Cursor works, but with this issue

6

Hey, thanks for the detailed report and for sharing a workaround right away.

Quick clarification: the built-in Markdown Preview in Cursor Cmd+Shift+V never had its own Mermaid rendering. Just like in VS Code, it relies on third-party extensions like bierner.markdown-mermaid. So this isn’t a bundled-version regression. It’s a feature gap, since native parity with VS Code 1.121 in the standard preview isn’t there yet.

Important detail: in-app rendering in Cursor in chat, plans, and composer uses a modern Mermaid version and supports C4 diagrams like C4Container, Boundary, ContainerDb, Rel, and so on correctly. The issue is only with the standard Markdown Preview.

Your workaround is valid. Even though bierner.markdown-mermaid is marked deprecated on the Marketplace, it still installs and works. Open it via Markdown: Open Preview from the extension command.

There’s already a request for native Mermaid support in the regular .md preview on the forum. I’ll merge this into it so votes count in one place: Feature Request: Enable Plan-style Mermaid rendering for regular .md files. No ETA yet, but it’s on the radar.