mcp_arguments_invalid

Arguments are not an object. Answered with 400.

What it means

A tool call's arguments member has to be a JSON object keyed by parameter name. Absent and null both mean "no arguments"; anything else – an array, a string, a number – is a call nobody could act on.

What to do

Send arguments as an object, e.g. {"arguments": {}}. The parameters a tool takes are in its inputSchema.

The body

{
  "type": "https://tigby.eu/problems/mcp_arguments_invalid",
  "title": "Arguments are not an object",
  "status": 400,
  "detail": "…what was refused, naming this request's own values",
  "code": "mcp_arguments_invalid",
  "doc_url": "https://docs.tigby.eu/errors/mcp_arguments_invalid",
  "agent_hint": "…the next step, for software"
}

Branch on code. The detail names this request's own Handle, id or limit and is not part of the contract.