Thing Syntax

Preview

DEFINE THING is a preview feature. It ships in broker 2.22. The syntax and behaviour may still change.

For what a Thing is and a first example, see Things Overview.

Templates and roots

Declaration	Meaning
`DEFINE THING TEMPLATE <name>`	A template. Stored, never deployed by itself
`DEFINE THING <name>`	A root. Adding it deploys its whole instance tree
`DEFINE THING <name> OF <template>`	A root that is one instance of a template. Only `WITH PARAM` lines may follow

OF must name a template. Naming a root or an unknown Thing is an error, and so is a cycle.
Templates are stored on the broker. A root added later, from another cell, notebook or project, can use a template added earlier.
DEFINE THING north OF Station puts Station’s clauses directly at north_<clause>. A plain root with WITH THING station OF Station adds a level: north_station_<clause>.

Clauses

A clause is a standalone declaration with DEFINE replaced by WITH, indented one level under the Thing. Every kind keeps its full syntax, so you can paste an existing definition into a Thing: indent it one level and change DEFINE to WITH.

Clause	Expands to
`WITH CONNECTOR <name> WITH TYPE <type>` (or `WITH ROUTE …`)	`DEFINE CONNECTOR`
`WITH MODEL <name> …`	`DEFINE MODEL`
`WITH ACTION <name>`	`DEFINE ACTION`
`WITH RULE <name> WITH PRIORITY n FOR …`	`DEFINE RULE`
`WITH AGENT <name>`	`DEFINE AGENT`
`WITH PANEL <name>`	`DEFINE PANEL`
`WITH THING <child> OF <template>`	One more instance of the template
`WITH PARAM <name> [value]`	Nothing. Declares a param

An action’s trigger, INPUT, DO and RETURN lines sit at the clause’s own level, exactly where they sit under a standalone DEFINE ACTION.
Python scripts and themes are not clauses.
Children deploy in the order connectors → models → agents → actions → rules → panels, and are removed in reverse.

Params and placeholders

Where	`WITH PARAM ip "10.0.0.5"` means	`WITH PARAM ip` means
In a template	A default	A required param
In a plain root	Its value	An error: a root param needs a value
Under `WITH THING … OF T` or `DEFINE THING r OF T`	An argument to `T`	An error

For each param, the broker uses, in order: the argument at the call site, then the template’s default, then (for a required param) the value in the nearest enclosing instance that has one. Otherwise the deploy fails and names the missing param.

An argument must name a param the template declares, or path.
An argument can use the caller’s placeholders: WITH PARAM ip "{{baseIp}}.11". Defaults are literals.
A value may not contain ", a line break or {{.
Keep secrets in GET SECRET and GET ENV inside clause bodies, never in params. Params are published with the Thing’s tree.

Reserved placeholders

Placeholder	Value
`{{thing}}`	The instance’s own name
`{{parent}}`	The parent instance’s name. Empty at the root
`{{path}}`	A topic prefix. By default the instance chain joined with `/` (`factory/line1/press1`). Set `WITH PARAM path "plant/north"` on a root to change it

Substitution is textual and happens before a clause is parsed, so a placeholder can sit in a string ("{{path}}/status") or a bare position (WITH SLAVE_ID {{slave}}). Placeholders are not allowed in Thing, child, clause or param names. Write \{{ for a literal {{. Single-brace {x} (action variables, {payload}, {env.NAME}) is never touched.

Names

Thing, instance and clause names match [A-Za-z_][A-Za-z0-9_]*. TEMPLATE can’t be a Thing name.
A child is named by the instance chain and the clause name joined with _: factory_line1_press1_modbus.
Every expanded name is checked before anything changes. A name owned by another Thing or project is an error.
An existing standalone entity of the same kind and name is adopted: the expanded declaration replaces it and the root owns it from then on.

References

A clause can refer to a clause of the same instance by its local name, or to a clause of a descendant by a dotted path (p1.Assistant). The broker rewrites these to expanded names in CALL ACTION, PUBLISH MODEL, GET MODEL, STORE IN, CALL AGENT, CALL LLM, CALL MCP, USES LLM CONNECTOR, WITH AGENTS, agent tool WITH TARGET, and panel bindings.

A single name that matches no sibling clause passes through unchanged, so a Thing can use a connector deployed outside it.
A dotted reference must resolve, or the Thing is rejected.
Topic strings and payloads are never rewritten.

To wire siblings together, declare a reference param: WITH PARAM peer AS AGENT (or AS CONNECTOR, MODEL, ACTION, PANEL). An argument resolves in the caller, so a parent can pass WITH PARAM peer "south.Lead" to its north child.

DEFINE THING TEMPLATE Cell
    WITH PARAM llm AS CONNECTOR
    WITH PARAM agentUser
    WITH PARAM peer AS AGENT
    WITH AGENT Lead
        USES LLM CONNECTOR {{llm}}
        WITH DEFAULT_USER "{{agentUser}}"
        WITH AGENTS "{{peer}}"
        WITH INTERACTION_TOPIC "{{path}}/lead"
        ADD TOOL "read_mqtt"
            WITH TOPICS "{{path}}/#"

DEFINE THING site
    WITH PARAM agentUser "agent-site"
    WITH CONNECTOR Brain WITH TYPE LLM
        ADD LLM_CONFIG
            WITH PROVIDER "anthropic"
            WITH MODEL "claude-sonnet-4-0"
            WITH API_KEY GET SECRET "ANTHROPIC_API_KEY"
    WITH THING north OF Cell
        WITH PARAM llm "Brain"
        WITH PARAM peer "south.Lead"
    WITH THING south OF Cell
        WITH PARAM llm "Brain"
        WITH PARAM peer "north.Lead"

agent-site must already exist as a broker user. LoT can’t create users.

Ownership

Children run, publish and can be called like any other entity. They are read-only except through their Thing:

Action 'Oven_inlet_Overheat' is owned by THING Oven (instance Oven/inlet, clause Overheat); edit the Thing instead.

-addAction, -removeConnector and the other per-entity commands are refused on a Thing-owned name. -removeAllConnectors, -removeAllModels and -removeAllActions keep owned children and list them as skipped.

Permissions

Operation	Permission
`-addThing`	`ThingManagementCreation`
`-removeThing`	`ThingManagementRemove`
`-listThings`	`CommandCall`

Every child is also checked against its own kind’s permission, as if you added it directly. One missing permission rejects the whole unit. Children also count toward license limits.

Troubleshooting

Symptom	Fix
`… is owned by THING …; edit the Thing instead.`	Change the clause and redeploy the Thing
`Template 'X' is used by …` on `-removeThing`	Remove or change the Things that use it first
`OF` error naming a root	Mark the target `DEFINE THING TEMPLATE`
Unresolved placeholder	Declare the param, or pass it
A child error points at the Thing line	Run `-addThing --dryRun` and read that child’s expanded `code`

Quick Start

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Templates and roots

Clauses

Params and placeholders

Reserved placeholders

Names

References

Ownership

Permissions

Troubleshooting

​Templates and roots

​Clauses

​Params and placeholders

​Reserved placeholders

​Names

​References

​Ownership

​Permissions

​Troubleshooting

Templates and roots

Clauses

Params and placeholders

Reserved placeholders

Names

References

Ownership

Permissions

Troubleshooting