Error reference
Mermaid errors, decoded
Mermaid's parser errors are accurate but cryptic. This reference translates the raw error text into plain language: what actually broke, why, and how to fix it — each one verified against a real Mermaid 11 parse, not guessed.
Parse error: got 'CALLBACKNAME'
A node ID exactly matches a Mermaid keyword (call, click, or href) and is referenced without a shape, so the parser reads it as a click-callback token instead of a node name.
Parse error: got 'SQS'
A node's square-bracket label was never closed, so the parser runs into the next node's opening bracket before it finds the one it was expecting.
Parse error: got 'PS'
A square-bracket label contains a raw ( or ), which Mermaid reads as the start of a different node shape rather than as label text.
Parse error: got 'MINUS'
An edge uses a single-dash arrow (->) instead of Mermaid's two-dash flowchart arrow (-->).
No diagram type detected
The source doesn't start with a Mermaid diagram keyword, so the renderer has nothing to match against any known grammar.
Trying to inactivate an inactive participant
A deactivate call has no matching activate for that participant, so Mermaid has no active lifeline to turn off.
ER diagram parse error: got 'IDENTIFYING'
A relationship line uses a plain arrow or dash instead of Mermaid's crow's-foot cardinality notation, which erDiagram requires on every relationship.
State diagram parse error: got 'INVALID'
A transition between two states uses a single dash instead of stateDiagram's arrow (-->), the same class of mistake as the flowchart single-dash trap.
Parse error: got 'NODE_STRING'
A node ID contains an unquoted space before its shape, so Mermaid reads it as two separate statements instead of one node.
sequenceDiagram parse error: missing end for a block
An alt, loop, opt, par, critical, or break block was opened but never closed, so the parser runs out of diagram before it finds the matching end.
Class diagram parse error: got 'ALPHA'
A relationship arrow is missing a dash, so Mermaid can't recognize it as one of the defined class relationship types.