# Cross-Runtime Capability Parity **Domain:** Interoperability / Programming Languages **Doc Type:** Canonical Concept Node **Maturity:** Developing **Related:** [[wiki/Portable Contract|Portable Contract]], [[wiki/Conformance Testing|Conformance Testing]], [[wiki/Host Adapter|Host Adapter]] --- ## Definition **Cross-runtime capability parity exists when implementations in different languages expose the same capability contract and produce equivalent normalized observations.** Parity concerns behavior, not identical internal code or identical host features. ## Project Context X pursued aligned functions across browser JavaScript, Node, PHP, and planned Python and Perl surfaces. Pure transformations can approach full parity. Filesystem, network, editor, and database operations require host adapters and may support explicitly different capability sets. ## Key Insight **Parity is not sameness of implementation; it is agreement at the contract boundary.** ## See Also [[projects/X and XApps - Drop the Folder and It Runs|X and XApps]], [[wiki/Deterministic Transformation|Deterministic Transformation]], [[wiki/Capability Registry|Capability Registry]], [[wiki/Technical Terms|Technical Terms]]