Wire Encoding

Delta-MCP negotiates a wire encoding at initialize. Both sides switch codecs after the handshake — the initialize response itself is always plain JSON so the client can read it before the switch.

Compact-JSON

Key names are shortened to single characters:

Standard: {"jsonrpc":"2.0","method":"tools/list","result":{"tools":[...]}}
Compact:  {"j":"2.0","m":"tools/list","r":{"t":[...]}}

Compact-JSON reduces payload size by 18.7% on a 6-tool tools/list response. No behavior change — just shorter keys on the wire.

CBOR (HTTP only)

Binary encoding available over HTTP via the optional cbor-x dependency. Stdio clamps to compact-JSON because CBOR is binary and cannot be safely newline-delimited.

The HTTP transport decodes requests by Content-Type and encodes responses by the client’s Accept header.

Negotiation flow

Client advertises encoding capabilities at initialize:

// client sends:
capabilities: {
  encoding: { compactJson: true, cbor: true }
}

// server echoes the negotiated format:
{
  encoding: { format: "compact-json" }
}

Both sides switch to the negotiated codec for all subsequent messages. The initialize exchange itself stays in plain JSON so neither side needs to guess the codec before the handshake completes.

Fallback

Clients that don’t advertise encoding capabilities receive standard JSON — fully compatible with the MCP 2025-11-25 baseline. No configuration required on either side.