Introducing MCP4Unreal: 989 contracts and an honest catalog

Why this exists

Every MCP-for-Unreal plugin we looked at advertised a tool count and stopped there. Nobody published the fixtures. Nobody reported which tools actually mutate the editor, which return a plan, and which are stubs. So we built one that does.

Current public numbers are 989 callable contracts across 126 domains. The latest full package baseline is v0.9.69, which passed every release gate on 2026-06-15. v0.9.70 is the source patch that closes review debt and still needs package/install/runtime recertification.

What HonestStub means

A tool is a HonestStub when the handler is wired up, the schema is real, but the editor operation it claims to perform is not actually implemented. Most catalogs call these “supported”. We call them what they are and flag them in every response.

PlanningOnly

Some tools intentionally return a plan instead of mutating. Dry-run spawns, proposed transforms, or migration previews. Every response declares the PlanningOnly state so the caller does not mistake a preview for a commit.

The validation pipeline

Direct and route coverage is currently 1001/1001. Fixtures run against a clean project, reports are archived per release, and a regression fails the release gate.

Transaction modes

Three modes, reported on every call: execution_scoped, handler_owned, not_applicable. Callers always know whether the editor undo stack captured the change.

What comes next

v1.0 will add the hosted docs site, the tool catalogue explorer, and the signed sweep report viewer. Validation evidence ships with every release.