Mermaid errors from full-width punctuation and look-alike characters

The short answer

Mermaid's syntax characters must be plain ASCII: brackets, colons, semicolons, quotes and arrows. Punctuation inside a label can be anything. Errors appear when the characters that define a shape or a link are full-width or typographic variants.

Which characters to replace

Breaks the code	Correct	Used for
（ ） 【 】	( ) [ ]	Node shapes
｛ ｝	{ }	Decision diamonds
：	:	Sequence messages, Gantt tasks
；	;	End of a statement
“ ”	"	Quoting text with special characters
－－＞ ——>	-->	Links

A typical example

Three full-width characters stop this from rendering:

flowchart TD
    A【Submit】 --> B｛Approved?｝
    B －－＞ C（Done）

With ASCII characters it works:

flowchart TD
    A[Submit] --> B{Approved?}
    B --> C(Done)

Hyphens that only look right

Dates and style names in AI replies sometimes use a non-breaking hyphen, which looks like - but is a different character: 2026‑10‑01, stroke‑width. A Gantt chart reports an invalid date and a flowchart reports an unrecognized character. Retype them with a plain -.

When a label needs brackets

To show ASCII brackets or quotes in a label, wrap the whole label in double quotes:

flowchart LR
    A["Submit (with attachments)"] --> B["Review (1-3 business days)"]

Skip the hunt

Paste the code or the whole AI reply into the editor. Full-width brackets, colons, arrows and look-alike hyphens are detected, and "Fix it" in the status row replaces them all. Each error is explained in Common errors.