HTTP-level compression technique that uses a pre-shared dictionary of commonly occurring tokens (e.g. all JSON keys across an API surface, enum values) to compress requests and responses. Because it operates at HTTP level, it applies to JSON APIs — REST, GraphQL, and potentially MCP — as well as other text resources. With a well-chosen dictionary, payload sizes can approach Protocol Buffers on the wire, offering a middle ground between REST's flexibility and gRPC's efficiency; the serialization/deserialization overhead remains. Requires client-side implementation and the dictionary must contain no personally identifiable information. Raised by Ryan Townsend from the audience at the wroclove.rb 2026 Q&A as a way to get close to gRPC performance without the rigidity of a protofile contract.