Utilities — Logging, Progress, Cancellation, Completion

Logging

Servers emit notifications/message with a syslog-style LoggingLevel (RFC 5424). Clients filter via logging/setLevel.

{
  "jsonrpc": "2.0",
  "method": "notifications/message",
  "params": { "level": "warning", "logger": "auth", "data": "Rate limit close" }
}

Progress

To opt into progress updates, the requester puts a progressToken in params._meta. The receiver then emits notifications/progress carrying the same token.

{
  "method": "tools/call",
  "params": {
    "_meta": { "progressToken": "abc123" },
    "name": "long_operation",
    "arguments": {}
  }
}

{
  "method": "notifications/progress",
  "params": { "progressToken": "abc123", "progress": 50, "total": 100, "message": "Indexing..." }
}

• progress MUST increase monotonically.
• total is optional — omit if unknown.
• Each in-flight request needs its own unique token.

Cancellation

Best-effort cancellation: either side sends notifications/cancelled with the request id. Receivers MAY stop work; cancellation is not guaranteed.

{
  "method": "notifications/cancelled",
  "params": { "requestId": 7, "reason": "User pressed Stop" }
}

Argument completion

Clients call completion/complete as the user types arguments for a prompt or resource template. Servers return up to 100 suggestions plus optional total and hasMore.

The _meta field

Reserved on most objects for custom metadata. Use reverse DNS keys (com.example/feature). Prefixes starting with io.modelcontextprotocol/ or mcp/ are reserved. The OpenTelemetry trace keys (traceparent, tracestate, baggage) are special — no prefix required.