Event Schema

mcpr emits newline-delimited JSON events when started with --events. Each event has a type field and common metadata.

Common fields

Every event includes:

Field	Type	Description
ts	string	ISO 8601 timestamp
type	string	Event type (see below)
session	string	MCP session ID
upstream	string	Upstream server URL
csp_applied	boolean	Whether CSP headers were injected

tool_call

Emitted when an MCP tool is called.

{
  "ts": "2026-04-02T10:15:30.142Z",
  "type": "tool_call",
  "method": "tools/call",
  "tool": "search_products",
  "session": "sess_abc123",
  "user": null,
  "latency_ms": 142,
  "status": "ok",
  "upstream": "http://localhost:9000",
  "csp_applied": true
}

Field	Type	Description
method	string	JSON-RPC method (tools/call)
tool	string	Tool name
latency_ms	number	Total round-trip time in milliseconds
status	string	ok or error
user	string | null	Authenticated user (when OAuth is enabled)
error_code	number	JSON-RPC error code (present if status is error)
error_message	string	Error description (present if status is error)

tool_list

Emitted when a client requests the tool list.

{
  "ts": "2026-04-02T10:15:30.000Z",
  "type": "tool_list",
  "method": "tools/list",
  "session": "sess_abc123",
  "latency_ms": 11,
  "status": "ok",
  "upstream": "http://localhost:9000"
}

session_start

Emitted when a new MCP session is initialized.

{
  "ts": "2026-04-02T10:15:29.500Z",
  "type": "session_start",
  "session": "sess_abc123",
  "upstream": "http://localhost:9000"
}

session_end

Emitted when a session closes.

{
  "ts": "2026-04-02T10:20:00.000Z",
  "type": "session_end",
  "session": "sess_abc123",
  "upstream": "http://localhost:9000"
}

widget_serve

Emitted when widget HTML is served through the proxy.

{
  "ts": "2026-04-02T10:15:31.000Z",
  "type": "widget_serve",
  "path": "/widget/clock.html",
  "session": "sess_abc123",
  "upstream": "http://localhost:4444",
  "csp_applied": true
}

csp_violation

Emitted when a Content Security Policy violation is detected.

{
  "ts": "2026-04-02T10:15:32.000Z",
  "type": "csp_violation",
  "blocked_uri": "https://cdn.example.com/script.js",
  "directive": "script-src",
  "session": "sess_abc123",
  "upstream": "http://localhost:9000"
}

Field	Type	Description
blocked_uri	string	The URI that was blocked by CSP
directive	string	The CSP directive that caused the violation