Mermaid timeline diagrams fail to render in Cursor Chat

Support Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

In Cursor Chat, Mermaid fenced code blocks using the timeline diagram type never render as a diagram. The same Chat session successfully renders other Mermaid types such as flowchart.
This is not caused by diagram text content (Chinese characters, full-width parentheses, %, emoji, duplicate period labels, etc.). A minimal ASCII timeline also fails, while an adjacent flowchart renders correctly.
Independent validation: the failing timeline source parses successfully with [email protected] (mermaid.parse(...) returns PASS).

Steps to Reproduce

  1. Open a Cursor Chat conversation.
  2. Ask the agent (or paste) the three Mermaid blocks below in one reply.
  3. Observe which blocks render as diagrams.

A — minimal timeline (fails)

timeline
    title Minimal Timeline
    2026-07-22 10h00 : event A
    2026-07-22 10h12 : event B

B — realistic case timeline (fails)

timeline
    title Trip Timeline (Asia/Hong_Kong)
    2026-07-22 10h00 : Checked in at hotel lobby (Hotel App)
    2026-07-22 10h12 : Entered subway station Gate A (Transit App)
    2026-07-22 10h18 : Exited subway station Gate B (Transit App)
    2026-07-22 10h18 : Photo check-in at museum entrance (Maps)
    2026-07-22 10h25 : Arrived at cafe near exit C (Maps)

C — flowchart control (works)

flowchart LR
    A[C] --> B[I]
    B --> C[CM]

Expected Behavior

  • Content hypotheses ruled out: full-width parentheses （）, %, warning emoji :warning:, en-dash –, duplicate identical period labels — all parse on [email protected].

  • Confirmed real syntax footgun (not present in the failing sample): colon inside period labels such as 10:00 breaks Mermaid timeline parsing; the sample uses 10h00 and still fails in Cursor Chat.

  • Conclusion: failure is tied to diagram type support / loader registration for timeline in the Chat renderer, not to the specific event text.

Screenshots / Screen Recordings

A_test.png
A_test.png1574×347 18 KB

Operating System

Windows 10/11

Version Information

Version: 3.12.30 (user setup)
VS Code Extension API: 1.128.0
Commit: 63a2996a10d9e476b6c28e951dd7691d9c0cf480
Date: 2026-07-21T22:50:03.568Z
Layout: IDE
Build Type: Stable
Release Track: Default
Electron: 40.10.3
Chromium: 144.0.7559.236
Node.js: 24.15.0
V8: 14.4.258.32-electron.0
xterm.js: 6.1.0-beta.256
OS: Windows_NT x64 10.0.26200

Additional Information

Official Mermaid docs still mark Timeline as experimental. Several hosts historically failed to render timeline/mindmap when lazy-loaded diagram modules were not registered or async render paths were incomplete. Cursor Chat appears to support modern types such as C4 in-app, but timeline currently does not render in Chat in this environment.

Does this stop you from using Cursor

No - Cursor works, but with this issue

5

Hey, thanks for the detailed report with a minimal repro and a control case. I reproduced it and I’m seeing the same thing.

You’re right, it’s not about the diagram content, it’s about type support. The Mermaid renderer in Chat currently supports a limited set of types: flowchart, stateDiagram, sequenceDiagram, classDiagram, erDiagram, and xychart. Types like timeline (and also gitGraph, pie, gantt, mindmap, journey, C4) aren’t supported and fall back to the flowchart parser. That’s why you get a misleading “Mermaid Syntax Error” instead of a clearer “unsupported type” message.

This is a known limitation and I’ve reported it internally. I can’t share an ETA for a fix yet.

As a workaround, for timeline-like data you can use a supported type, like flowchart LR with a sequence of nodes, or sequenceDiagram. If there’s an update, I’ll follow up in the thread.