Is it Rig?

Rig is a shared vocabulary - Readable Independent Grammar: the schema catalog (prose + JSON Schema) and portable entity + POD component documents (rig.document). It is not a library to link into your app.

A project is Rig when:

It speaks portable meaning as entities with POD components keyed by schema ids (rig.<domain>.<name>).
It ships the schemas it supports - ship what you support.

That composition model is the floor. No entity/component POD, no Rig. A SUDE loop by itself is a loop convention, not a shared vocabulary.

Schemas and UI are optional beyond what you implement. rig-validate checks emission against the machine grammar - including rig.ui.* when present.

Live hosts

A live host (a program that runs creative work over time) typically honors the SUDE loop and runtime ECS conventions (registry, Update/Draw systems). RigKit takes SUDE + ECS as its floor - required to be RigKit, not required to be Rig. Validators, converters, and static presenters can be Rig without SUDE. See ecs.md for the split between document composition (Contract floor) and runtime systems (live hosts).

Rig + UI (optional)

A project is Rig + UI when it already is Rig and author/tool surfaces edit the same entity POD through a host seam (not a second scene graph). Full checklist: ui.md. Omitting UI remains valid Rig. Layout chrome and UI packs are fulfillment - portable meaning is rig.ui.* in the document.

What you may omit

Any host, any UI, any pack, device drivers, render backends, SUDE (unless you are RigKit or another host that claims the loop), and every schema you do not implement. You do not need a particular implementation to be Rig.

Reference fulfillment

RigKit is the reference live host: a desktop fulfillment (GLFW / OpenGL / packs) that runs the SUDE loop, owns an ECS registry, and reads and writes the schemas it supports. Read it as one worked answer, not as the definition - see terms.md for what "fulfillment" claims and does not claim.