How to Preview Markdown and Mermaid in Cursor

Cursor can edit a Markdown file and show a formatted preview beside the source. That makes it convenient for README files, implementation plans, and technical documentation that live in a code repository. The basic preview is only the first part of the workflow, however. Mermaid diagrams introduce a second question: does the preview actually render the diagram, or does it only display the fenced source block?

This guide focuses on previewing Markdown and Mermaid in Cursor, checking feature support, and validating the final document without turning the task into a general editor comparison.

Open the Markdown Preview in Cursor

Open a .md file in Cursor, then use the Markdown preview command from the Command Palette. You can also open the preview to the side so the source and rendered result remain visible together.

A side-by-side layout is useful for ordinary Markdown:

• Edit a heading and confirm its hierarchy.
• Fix a list and check its indentation.
• Update a table and inspect its columns.
• Change a relative link and test its destination.
• Edit a fenced code block and check its language highlighting.

If a keyboard shortcut differs on your operating system or keymap, search for “Markdown: Open Preview” in the Command Palette rather than relying on a memorized shortcut.

Test Mermaid With a Minimal Diagram

Start with a small known-good block. This separates preview support from errors in a large diagram.

```mermaid
flowchart LR
  Draft[Edit in Cursor] --> Preview
  Preview --> Review{Diagram visible?}
  Review -->|Yes| Continue[Check the full document]
  Review -->|No| Support[Check Mermaid support]
```

Open the Markdown preview and inspect the result. There are three common outcomes:

1. The diagram renders as shapes and arrows. Mermaid rendering is active.
2. The block appears as highlighted text. Markdown works, but Mermaid rendering is not active in that preview.
3. An error replaces the diagram. Mermaid is active, but the source or supported Mermaid version needs attention.

This distinction matters. Installing another extension will not repair invalid syntax, and editing the diagram will not enable a preview engine that treats Mermaid as plain code.

When Mermaid Appears as Code

A fenced block labeled mermaid is valid Markdown even when a viewer cannot turn it into a diagram. Basic Markdown engines deliberately preserve unknown fenced languages as code. That protects the source, but it can make a document look complete when a large piece of information is still unreadable.

Check these points:

• The opening fence contains exactly mermaid after the backticks.
• The closing fence is present.
• The preview or installed extension explicitly supports Mermaid.
• The workspace trusts the extension and permits scripts it needs.
• The diagram type is supported by the bundled Mermaid version.

Avoid enabling a collection of overlapping preview extensions at once. Two extensions can register similar preview commands or use different Mermaid versions, making failures harder to reproduce. Choose one preview path, test it, and document it for the team.

When the Diagram Reports a Syntax Error

Reduce the diagram until the failing statement becomes clear. Frequent causes include reserved words used as node IDs, malformed arrows, quotes inside labels, incomplete subgraphs, and syntax introduced in a newer Mermaid release.

For example, prefer a safe node ID with a separate label:

The rendered label can say “End” without using a potentially troublesome word as the identifier. If the block is hard to isolate inside a long file, paste only that diagram into Mermaid Studio. The guide to fixing a broken Mermaid diagram covers a render-validated repair workflow.

Preview the Document, Not Only the Diagram

A successful Mermaid render does not prove that the complete Markdown file is ready. Technical documents combine several rendering systems:

Content	What to verify
Mermaid	Diagram renders; labels are readable
Tables	Columns align and remain usable when wide
Links	Anchors and relative paths resolve
Images	Local and repository paths load
Math	Inline and display formulas render
Code	Fences close and languages highlight

Check the document at a narrow width as well as a wide editor pane. Large diagrams and tables often look acceptable with half the screen available but overflow on a laptop, browser, or PDF page.

Cursor Preview Versus the Final Reading Environment

An editor preview is optimized for writing. The final reader may use GitHub, a documentation site, a browser link, or a PDF. Those environments can run different Markdown and Mermaid versions, apply different CSS, and resolve relative files from different locations.

Use Cursor's preview for the fast editing loop, then test the environment in which people will consume the document. For a GitHub README, follow the README preview checklist. For a standalone technical document, open it in a Markdown viewer with Mermaid support and check the document as one continuous page.

A Reliable Cursor Workflow

1. Open the .md source in Cursor.
2. Open Markdown preview to the side.
3. Test one minimal Mermaid diagram.
4. Enable one trusted Mermaid-capable preview path if necessary.
5. Repair syntax errors in isolation.
6. Review tables, links, images, formulas, and code fences.
7. Validate the document in its final reading environment.
8. Check the rendered result before printing or sharing.

Cursor is a strong place to edit Markdown because the source, repository, and preview can stay together. Treat its preview as a rapid authoring check, and treat the final renderer as the compatibility check. That boundary prevents a diagram that worked on one developer's machine from becoming raw code for everyone else.