Skip to content
Delta-MCP

ADR-001: Do Not Fork JSON-RPC 2.0

Status: Accepted — 2026-06-08

Context

Delta-MCP targets 78%+ input token reduction. The naive approach is to invent a new binary protocol. The risk: breaking compatibility with 97M+ monthly downloads of the MCP ecosystem.

Decision

Keep JSON-RPC 2.0 as the wire envelope. All Delta-MCP improvements (progressive disclosure, compact encoding, result handling) are implemented as:

  1. Negotiated capabilities at initialize
  2. New optional methods (tools/describe)
  3. Optional encoding negotiated at handshake

Standard MCP clients that don’t negotiate Delta-MCP capabilities receive standard MCP behavior — unmodified.

Consequences

  • Full backward compatibility with existing MCP servers and clients
  • Delta-MCP capabilities can be submitted as an MCP Extension (2026-07-28 Extensions framework)
  • Slightly more complexity in server: must handle both standard and progressive modes
  • Cannot use binary-only optimizations without a JSON fallback path