Learn the small Schemd grammar

01 / NodesPlace a component on a bounded canvas

Every fence opens with a promise about space: bounds="WIDTHxHEIGHT", both integers from 64 to 4096. The compiler reserves that canvas before reading a single declaration, which is why a schemd diagram never reflows the page it lands on.

A node has one predictable shape:

kind:ID "label" at (x, y) color [options]

IDs are case-sensitive, coordinates live in the viewBox we just declared, and the [options] depend entirely on the kind we chose. The colour is a built-in token such as #blue, a safe CSS colour, or a theme alias we resolve ourselves.

port:VIN "Signal" at (60, 160) #blue
resistor:R1 "10 k\Omega" at (250, 160) #amber
capacitor:C1 "100 nF" at (470, 160) #cyan
port:VOUT "Filtered" at (700, 160) #emerald

VIN.out -> R1.in #blue [line]
R1.out -> C1.in #amber [ortho]
C1.out -> VOUT.in #emerald [line marker-end=arrow]

02 / ConnectionsConnect named ports

A connection is just as small — two named ports and an arrow:

ID.port -> ID.port color [options]

Then choose how the wire travels: line for a straight segment, bezier for a curve, ortho for the obstacle-aware route. An orthogonal connection escapes each component through a short stub, clears every other node's bounds, and — this is the part that matters — fails loudly when no clear path exists rather than drawing a junction that lies about the circuit.

Markers are optional on either end: marker-start=... and marker-end=... accept none, arrow, open-arrow, dot, triangle, diamond, or diamond-filled.

port:A "A" at (60, 90) #blue
port:B "B" at (60, 250) #slate
xor:G1 "Parity" at (390, 170) #cyan [inputs=2 outputs=1]
port:Y "Result" at (720, 170) #emerald

A.out -> G1.in1 #blue [bezier]
B.out -> G1.in2 #slate [ortho]
G1.out -> Y.in #emerald [line marker-end=arrow]

03 / UMLUse relationship names instead of hand-built markers

A UML relationship is nothing more exotic than a connection option: name the relationship and schemd supplies the marker and dash pattern the notation already expects. Disagree with a default and an explicit marker — or a plain solid/dashed flag — overrides it.

Add label="text" whenever the connector needs a name of its own.

class:Account "Account" at (220, 150) #slate [attributes="- id: UUID" operations="+ close(): void"]
class:Admin "Admin" at (620, 120) #blue [operations="+ suspend(): void"]
class:Session "Session" at (620, 310) #emerald [attributes="- token: string"]

Admin.left -> Account.right #blue [ortho generalization]
Account.right -> Session.left #emerald [ortho composition label="owns"]