Sygil PBC This document specifies the Sygil Protocol, an open schema and query grammar for cross-domain personal data designed to make user data interoperable across systems, vendors, and AI agents. The protocol defines a content-addressable record envelope, a reverse-DNS namespace identifier scheme, a deterministic JSON canonicalization rule, an optional vocabulary of proof objects for conveying provenance and other trust evidence on the wire, a minimal query grammar, and three adoption tiers from envelope-shaped data through queryable surfaces to vault-certified runtimes. The protocol is runtime-neutral: it specifies what travels on the wire, not how implementations store, encrypt, authorize, or audit records. This separation lets independent systems produce, consume, and exchange Sygil-shaped data without depending on any specific vault infrastructure.