Lua Node Authoring Guide

New to Computed? The Getting Started tutorial shows the editor basics first. This page is about writing your own nodes in Lua.

Every Computed node is a Lua definition. A file creates one node, declares an immutable schema, installs callbacks, and returns that node.

local node = computed.node(1, "example:counter", "Counter")

node:category("state")
node:style("standard")
node:input("increment", "number")
node:output("count", "number")
node:field("step", "number", {
    default = 1,
    min = 0,
    max = 10,
    control = "slider",
    step = 0.5,
    label = "Step Size"
})
node:state("count", 0)

node:on_run(function(ctx)
    local next = ctx:state("count") + ctx:input("increment") * ctx:field("step")
    ctx:set_state("count", next)
    ctx:output("count", next)
end)

return node

Definition IDs are stable, lowercase, namespaced identifiers. Port, field, state, and event IDs start with a lowercase letter and contain only lowercase letters, digits, _, ., or -. Schemas cannot change while an instance is running.

Choose input execution for dataflow nodes, tick for world sensors, step for explicitly stepped nodes, and event when only named handlers should run. A failed invocation discards all staged output and state changes. The next eligible execution retries the callback.

For user-authored wireless graph flow, see Graph events. Lua callbacks can inspect configurable per-instance inputs with ctx:inputs().

Use endpoints for Minecraft or addon access. Lua values never contain Java or Minecraft objects.

Create a node in a computer

Open the Node Explorer, expand User Nodes, and choose New Lua Node…. The editor starts with a unique reusable user:node_<id> definition. Edit and preview the source, then choose Save. Computed adds the validated definition to that computer's embedded library and places its first instance at the canvas anchor. Additional instances appear under User Nodes and can be placed like bundled nodes.

Right-click an existing definition in the explorer to edit it. Replacing a definition with the same ID requires confirmation when its source hash changes.

Field controls

Field values belong to each node instance and participate in autosave, undo, duplication, and server validation. Use value controls for unrestricted numbers and explicit sliders for bounded values:

node:field("name", "text", { default = "Display" })
node:field("enabled", "boolean", { default = true })
node:field("side", "direction", { default = "front" })
node:field("mode", "choice", {
    default = "normal",
    choices = { "normal", "inverted" }
})
node:field("speed", "number", {
    default = 10,
    min = 0,
    max = 20,
    control = "slider",
    step = 1
})

See Lua API Reference, Types and State, Sandbox and Budgets, and the examples in the repository.