Critical Performance Degradation and UX Regression in Markdown Preview

[sigmadream (Han Sangkon)]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

I am reporting a significant regression in both User Experience and performance regarding the Markdown preview functionality. The current implementation forces a preview mode upon clicking a file and suffers from unacceptable performance issues that freeze the editor.

1. The decision to display the Preview by default when a Markdown file is clicked is counter-intuitive for a code editor. Users open files primarily to edit them, not just to view a rendered version.
2. Even with a relatively small 135kb Markdown file, the preview engine causes the entire editor to hang/freeze.
3. This file opens and renders instantly in legacy editors like vi, Emacs, VS Code, and even basic tools like Windows Notepad. It is baffling that a modern, AI-powered IDE like Cursor fails where basic text editors succeed.
4. If the team intends to prioritize the Preview mode, it must be robust enough to handle standard file sizes without crashing the UI thread.

Could you clarify why the editor’s default behavior was set to ‘Preview’? From a user perspective, this decision is still a bit regrettable.

Steps to Reproduce

1. Select a Markdown file (~135kb) from the file explorer.
2. Observe the editor defaulting to “Preview” mode instead of the source editor.
3. Observe the editor becoming unresponsive or freezing during the rendering process.

Expected Behavior

1. Clicking a file should open the Source Editor by default.
2. If a preview is triggered, it should be rendered asynchronously without blocking the main editor thread.
3. Performance should be at least on par with standard VS Code or other text editors.

Screenshots / Screen Recordings

Operating System

MacOS

Version Information

Version: 2.4.28
VSCode Version: 1.105.1
Commit: f3f5cec40024283013878b50c4f9be4002e0b580
Date: 2026-02-03T00:56:18.293Z
Build Type: Stable
Release Track: Default
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Darwin arm64 25.2.0

Does this stop you from using Cursor

Yes - Cursor is unusable

[deanrie]

Hey, thanks for the detailed report. The team is aware of the default preview mode issue. But freezing while rendering a 135 KB file is odd.

First, let’s check extensions that might affect Markdown rendering:

1. CMD + Shift + P > Developer: Open Extension Monitor
   Take a look at what’s using CPU or memory.
2. Try running this from the terminal: cursor --disable-extensions
   Open the same file. Does the issue still happen?

If everything works with extensions disabled, then one of the extensions is causing it. If it still freezes, then it’s likely a bug in the core renderer.

Also, can you share:

• What kind of Markdown features are in the file (lots of tables, Mermaid diagrams, code blocks)?
• Which Markdown extensions do you have installed?

Let me know what you find, and we’ll decide the next steps.

[sigmadream (Han Sangkon)]

1. The Markdown includes the following elements:

   • Some LaTeX formulas

   • External URLs

   • Code blocks (C++, Bash)

   • It does not include any figures, images, or tables.

2. No extensions have been installed.

3. I hope it can be corrected(or fixed) properly.