Five common reasons a Mermaid mind map does not render

The short answer

A Mermaid mind map uses indentation alone for levels. The rules are few and strict: one root, equal indentation for siblings, and brackets in the text are read as shapes. These five cases cover nearly every failure.

1. More than one root

Only one line may sit at the outermost level. Two lines at the same outer level are two roots:

mindmap
  Revision plan
  Exam schedule

Move the second under the first, or add a root above both:

mindmap
  End of term
    Revision plan
    Exam schedule

2. Uneven indentation

Siblings need the same indentation and children need more than their parent. Mixing spaces and tabs is the usual culprit; use spaces only.

mindmap
  Reading notes
    Main ideas
      Idea one
      Idea two
    Quotes
    Actions

3. Brackets in the text

Name(detail) is read as an id plus a rounded shape, so unbalanced or nested brackets fail. Rephrase without brackets, or wrap the whole text in a shape:

mindmap
  root((Product launch))
    Market research
    ["Competitors (3 vendors)"]

4. Syntax that mind maps do not support

• Arrows -->: a mind map has no links, only indentation.
• classDef and style: custom style statements are not supported; change the theme for colors.
• Leading - , * or 1. : these are Markdown list markers, not mindmap syntax. Remove them.

5. The mindmap line appears twice

AI assistants sometimes split one map into two parts, each starting with mindmap. A diagram can have only one, so merge both parts under one root.

Let the editor fix it

The mind map page and the editor detect most of these: list markers, a repeated mindmap line and brackets in the text get a one-click "Fix it". The full syntax is in Mind map syntax, and ready-made structures are in the mind map templates.