Sequence Diagram

Core Diagram Type

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Mermaid Studio provides full language support for Sequence diagrams inside IntelliJ IDEA and other JetBrains IDEs. Sequence diagrams show how processes interact with each other over time, and are essential for documenting API flows, system integrations, and protocol specifications.

Syntax Highlighting

Syntax highlighting integrates directly with IntelliJ’s color scheme system, so diagram colors always match your editor theme.

Armada Dark

Islands Dark

Islands Light

IDE Support

Mermaid Studio provides comprehensive support for sequence diagrams:

• Syntax highlighting for participants and messages, with embedded-JSON highlighting inside properties and links blocks so the JSON keys and values stay readable.
• Code completion for participant names and message syntax. Top-level-only keywords (title, accTitle, accDescr, autonumber, properties, details, link, links) are filtered out inside control-flow blocks (loop, alt, opt, par, critical, break, rect) where Mermaid wouldn’t accept them.
• Live templates — 31 abbreviations covering block wrappers, notes, participants and actors (including typed-metadata @{type: ...} forms), messages (with a msg arrow-picker macro), and autonumber.
• Documentation hover for element information
• Rename refactoring to update participant names
• Find usages to locate participant references
• Code folding for every block keyword, including box and par_over.
• Formatting to clean up diagram structure. Empty box / loop / alt / rect no longer accumulate a blank line on every reformat, and a titleless box or rect keeps its first content line on its own row.
• Block-body isolation — a parse error inside one block body no longer cascades to its siblings or the rest of the file; each block reparses independently.
• Inspections to catch common errors:
  • Trailing whitespace after a @{...} participant / actor attributes block when no as follows (with a one-click fix to strip the space).
  • Non-participant / non-actor statements inside a box (Mermaid only renders box content of those two kinds).
  • Participant declared inside control flow (now covers par_over too) — with a quick fix that moves the declaration to top level.
  • Decimal autonumber values (autonumber 1.1 0.1) are validated and trailing whitespace on the autonumber statement is flagged on Mermaid 11.15.0+.
• Brace matching for block navigation. Pressing Enter inside inline properties / links JSON no longer triggers comma insertion or brace-pair expansion.
• Color provider for customizing diagram colors

Live templates

A set of 31 context-aware live templates scaffolds the block keywords, participant and actor declarations, notes, messages, and autonumber statements that sequence diagrams use day-to-day. Type a short abbreviation, accept it from the completion popup, and tab through the template variables.

Individual abbreviations can be toggled under Settings > Tools > Mermaid Studio > Live Templates in the Sequence Diagram group. See Live Templates for the cross-cutting mechanics (triggering, contextual visibility, configuration).

Block wrappers

Abbreviation	Expansion
bloop	loop ... end
balt	alt ... else ... end
bopt	opt ... end
bpar	par ... and ... end
bcrit	critical ... option ... end
bbrk	break ... end
bbox	Participant grouping box (box ... end)
brect	Background rectangle (rect rgb(...) ... end)

Notes

Abbreviation	Expansion
nl	Note left of participant
nr	Note right of participant
no	Note over participant

Participants and actors

The prta and atra templates produce as-aliased declarations; cprta and catra produce the create variants. The prj and atj templates use the typed-metadata @{type: ...} form (Mermaid 11.13.0+); cprj and catj produce the create variants of those.

Abbreviation	Expansion
prta	participant X as "Label"
atra	actor X as "Label"
cprta	create participant X as "Label"
catra	create actor X as "Label"
prj	participant X@{type: ...} (11.13.0+)
atj	actor X@{type: ...} (11.13.0+)
cprj	create participant X@{type: ...}
catj	create actor X@{type: ...}

Messages

msg is the generic form: it expands the arrow as a picker variable, so you choose the operator on insert. The other ten templates each hard-code one operator for when you already know the shape you want.

Abbreviation	Expansion
msg	Message with arrow picker (A -> B: text)
ms	Solid line, no arrowhead (A -> B: text)
msf	Solid line with arrowhead (A ->> B: text)
md	Dotted line, no arrowhead (A --> B: text)
mdf	Dotted line with arrowhead (A -->> B: text)
mc	Solid line with cross (A -x B: text)
mdc	Dotted line with cross (A --x B: text)
ma	Async solid arrow (A -) B: text)
mda	Async dotted arrow (A --) B: text)
mb	Bidirectional solid (A <<->> B: text)
mdb	Bidirectional dotted (A <<-->> B: text)

Autonumbering

Abbreviation	Expansion
autns	autonumber 10 10 (start + step)

Quick Syntax Reference

Participants

sequenceDiagram
    participant A as Alice
    participant B as Bob
    A->>B: Hello

Message Types

Syntax	Meaning
->	Solid line
-->	Dashed line
->>	Solid with arrowhead
-->>	Dashed with arrowhead
-x	Solid with cross
--x	Dashed with cross
<->>	Bidirectional
-)	Half-arrow (Mermaid 11.13.0+)
--)	Dashed half-arrow (Mermaid 11.13.0+)

Activation

sequenceDiagram
    Client->>+Server: Request
    Server-->>-Client: Response

Notes

sequenceDiagram
    Alice->>Bob: Hello
    Note right of Bob: Bob thinks
    Bob-->>Alice: Hi!

For full syntax details, see the Mermaid sequence diagram documentation.