Mermaid SystemContextDiagram Spec¶

Source: mermaid.system-context-diagram.json

This schema describes the SystemContextDiagram spec for the Mermaid backend.

Properties¶

Properties

Field	Type	Description
`type(required)`	`string`	Type of the diagram. Must be exactly `SystemContextDiagram`.
`title`	`string` \| `null`	Optional diagram title.
`elements`	`array[Element]`	Top-level elements.
`boundaries`	`array[Boundary]`	Top-level boundaries.
`relationships`	`array[MermaidRelationshipSchema]`	Top-level relationships.
`render_options`	`MermaidRenderOptionsSchema`	Mermaid-specific render options.
`backend(required)`	`string`	JSON schema backend. Must be exactly `mermaid`.

Examples

MinimalAdvanced

JSON source

{
  "backend": "mermaid",
  "type": "SystemContextDiagram",
  "elements": [
    {
      "type": "Person",
      "alias": "user",
      "label": "User"
    },
    {
      "type": "System",
      "alias": "app",
      "label": "My App"
    }
  ],
  "relationships": [
    {
      "type": "REL",
      "from": "user",
      "to": "app",
      "label": "Uses",
      "technology": "HTTPS"
    }
  ]
}

Rendered Mermaid source

C4Context

Person(user, "User")

System(app, "My App")

Rel(user, app, "Uses", "HTTPS")

Rendered image

JSON source

{
  "backend": "mermaid",
  "type": "SystemContextDiagram",
  "title": "Retail Platform",
  "elements": [
    {
      "type": "Person",
      "label": "Customer",
      "alias": "customer",
      "description": "Places orders through the storefront."
    },
    {
      "type": "PersonExt",
      "label": "Support Agent",
      "alias": "support_agent",
      "description": "Handles issues in an external CRM."
    },
    {
      "type": "SystemExt",
      "label": "Payment Gateway",
      "alias": "payment_gateway",
      "description": "Processes card payments."
    },
    {
      "type": "SystemExt",
      "label": "CRM Platform",
      "alias": "crm_platform",
      "description": "External CRM used by support agents."
    }
  ],
  "boundaries": [
    {
      "type": "EnterpriseBoundary",
      "label": "Acme Corp",
      "alias": "acme_enterprise",
      "description": "Internal systems owned by Acme.",
      "elements": [
        {
          "type": "System",
          "label": "Retail Platform",
          "alias": "retail_platform",
          "description": "Core platform for catalog, checkout, and order management."
        }
      ],
      "boundaries": [],
      "relationships": []
    }
  ],
  "relationships": [
    {
      "type": "REL",
      "from": "customer",
      "to": "retail_platform",
      "label": "Browses and places orders",
      "technology": "HTTPS"
    },
    {
      "type": "REL",
      "from": "retail_platform",
      "to": "payment_gateway",
      "label": "Charges card",
      "technology": "REST API"
    },
    {
      "type": "REL",
      "from": "support_agent",
      "to": "crm_platform",
      "label": "Manages customer issues",
      "technology": "Web UI"
    }
  ]
}

Rendered Mermaid source

C4Context
title Retail Platform

Person(customer, "Customer", "Places orders through the storefront.")

Person_Ext(support_agent, "Support Agent", "Handles issues in an external CRM.")

System_Ext(payment_gateway, "Payment Gateway", "Processes card payments.")

System_Ext(crm_platform, "CRM Platform", "External CRM used by support agents.")

Enterprise_Boundary(acme_enterprise, "Acme Corp", "Internal systems owned by Acme.") {
    System(retail_platform, "Retail Platform", "Core platform for catalog, checkout, and order management.")
}

Rel(customer, retail_platform, "Browses and places orders", "HTTPS")

Rel(retail_platform, payment_gateway, "Charges card", "REST API")

Rel(support_agent, crm_platform, "Manages customer issues", "Web UI")

Rendered image

Definitions¶

About labels and aliases

label is a display name for the element.

alias is a unique identifier used for referencing elements in relationships and layouts. If omitted, it is generated automatically.

You can also use label for referencing elements in relationships and layouts, but each label must be unique within the diagram.

RelationshipType¶

Relationship types supported by Mermaid C4 diagrams.

Items

Type	Description
`BI_REL`	A bidirectional relationship between two elements.
`REL`	A unidirectional relationship between two elements.
`REL_BACK`	A unidirectional relationship pointing backward.
`REL_D`	A unidirectional downward relationship. Shorthand for `REL_DOWN`.
`REL_DOWN`	A unidirectional downward relationship.
`REL_L`	A unidirectional leftward relationship. Shorthand for `REL_LEFT`.
`REL_LEFT`	A unidirectional leftward relationship.
`REL_R`	A unidirectional rightward relationship. Shorthand for `REL_RIGHT`.
`REL_RIGHT`	A unidirectional rightward relationship.
`REL_U`	A unidirectional upward relationship. Shorthand for `REL_UP`.
`REL_UP`	A unidirectional upward relationship.

DiagramElementPropertiesSchema¶

JSON schema for tabular diagram element properties.

Properties

Field	Type	Description
`header`	`array[string]`	Header columns. Default: `["Property", "Value"]`.
`properties(required)`	`array[array[string]]`	List of rows (each row is a list of string values).
`show_header`	`boolean`	Whether to display the header row. Default: `true`.

MermaidBoundarySchema¶

Mermaid JSON schema for a generic boundary.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `Boundary`.
`elements`	`array[Element]`	Elements may be nested arbitrarily.
`boundaries`	`array[Boundary]`	Boundaries may be nested arbitrarily.
`relationships`	`array[MermaidRelationshipSchema]`	Relationships declared inside the boundary.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.
`stereotype`	`string` \| `null`	Optional Mermaid boundary type/stereotype label.

MermaidEnterpriseBoundarySchema¶

Mermaid JSON schema for an enterprise boundary.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `EnterpriseBoundary`.
`elements`	`array[Element]`	Elements may be nested arbitrarily.
`boundaries`	`array[Boundary]`	Boundaries may be nested arbitrarily.
`relationships`	`array[MermaidRelationshipSchema]`	Relationships declared inside the boundary.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.
`stereotype`	`string` \| `null`	Optional Mermaid boundary type/stereotype label.

MermaidPersonExtSchema¶

Mermaid JSON schema for an external person.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `PersonExt`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

MermaidPersonSchema¶

Mermaid JSON schema for a person.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `Person`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

MermaidRelationshipSchema¶

JSON schema for relationships supported by Mermaid C4 diagrams.

Properties

Field	Type	Description
`type(required)`	`RelationshipType`	Type of the relationship.
`description`	`string` \| `null`	Additional details about the relationship.
`from(required)`	`string`	The source element alias (or unique label). For Mermaid, this must resolve to a concrete element, not a boundary.
`label(required)`	`string`	The label shown on the relationship edge.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.
`technology`	`string` \| `null`	The technology used in the communication.
`to(required)`	`string`	The destination element alias (or unique label). For Mermaid, this must resolve to a concrete element, not a boundary.

MermaidSystemBoundarySchema¶

Mermaid JSON schema for a system boundary.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `SystemBoundary`.
`elements`	`array[Element]`	Elements may be nested arbitrarily.
`boundaries`	`array[Boundary]`	Boundaries may be nested arbitrarily.
`relationships`	`array[MermaidRelationshipSchema]`	Relationships declared inside the boundary.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.
`stereotype`	`string` \| `null`	Optional Mermaid boundary type/stereotype label.

MermaidSystemDbExtSchema¶

Mermaid JSON schema for an external database-like system.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `SystemDbExt`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

MermaidSystemDbSchema¶

Mermaid JSON schema for a database-like system.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `SystemDb`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

MermaidSystemExtSchema¶

Mermaid JSON schema for an external software system.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `SystemExt`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

MermaidSystemQueueExtSchema¶

Mermaid JSON schema for an external queue-like system.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `SystemQueueExt`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

MermaidSystemQueueSchema¶

Mermaid JSON schema for a queue-like system.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `SystemQueue`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

MermaidSystemSchema¶

Mermaid JSON schema for a software system.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `System`.
`alias`	`string` \| `null`	Unique identifier for the element. If not provided, it is autogenerated from the label.
`description`	`string` \| `null`	Optional description text.
`label(required)`	`string`	Display name for the element.
`properties`	`DiagramElementPropertiesSchema`	Optional property table metadata.

Mermaid Render Options¶

MermaidRenderOptionsSchema¶

Final layout configuration for rendering a Mermaid C4 diagram.

Encapsulates layout directives, macros, tag definitions, and visual styles applied at render time.

Properties

Field	Type	Description
`styles`	`array[MermaidElementStyleSchema\|MermaidRelStyleSchema]`	List of style update macro configurations.
`update_layout_config`	`UpdateLayoutConfigSchema`	Configuration for updating default layout behavior.

MermaidElementStyleSchema¶

Style update for an individual diagram element.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `ElementStyle`.
`bg_color`	`string` \| `null`	Background color.
`border_color`	`string` \| `null`	Border line color.
`element(required)`	`string`	Alias of the element to style.
`font_color`	`string` \| `null`	Font/text color.

MermaidRelStyleSchema¶

Style update for relationship lines.

Properties

Field	Type	Description
`type(required)`	`string`	Discriminator identifying the element type. Must be exactly `RelStyle`.
`from_element(required)`	`string`	Alias of the source element to style.
`line_color`	`string` \| `null`	Color of the relationship line.
`offset_x`	`integer` \| `null`	Optional horizontal offset for the label position.
`offset_y`	`integer` \| `null`	Optional vertical offset for the label position.
`text_color`	`string` \| `null`	Color of the relationship label text.
`to_element(required)`	`string`	Alias of the target element to style.

UpdateLayoutConfigSchema¶

Configuration for updating default layout behavior in Mermaid C4 diagrams.

Properties

Field	Type	Description
`c4_boundary_in_row`	`integer` \| `null`	Maximum number of boundaries per row.
`c4_shape_in_row`	`integer` \| `null`	Maximum number of non-boundary elements (e.g. systems, containers, components) per row.

Mermaid SystemContextDiagram Spec¶

Properties¶

Elements¶

Boundaries¶

Relationships¶

Definitions¶

RelationshipType¶

DiagramElementPropertiesSchema¶

MermaidBoundarySchema¶

MermaidEnterpriseBoundarySchema¶

MermaidPersonExtSchema¶

MermaidPersonSchema¶

MermaidRelationshipSchema¶

MermaidSystemBoundarySchema¶

MermaidSystemDbExtSchema¶

MermaidSystemDbSchema¶

MermaidSystemExtSchema¶

MermaidSystemQueueExtSchema¶

MermaidSystemQueueSchema¶

MermaidSystemSchema¶

Mermaid Render Options¶

MermaidRenderOptionsSchema¶

MermaidElementStyleSchema¶

MermaidRelStyleSchema¶

UpdateLayoutConfigSchema¶