Model Context Protocol

Requirement An MCP server MUST pass an instructions value at initialize stating its transport, its audience, its write surface, and its refusal behavior.

Rationale The MCP specification's initialize response carries server instructions. A client loads them once per session and loads each tool description per call. Scope and policy therefore belong at the server level. They hold for every call. Tool mechanics stay in the tool descriptions. The model reads them when it chooses.

Example "Runs over stdio, one account per process, against the hosted API. Reads cover the account's own data, and three tools create or change records. A policy refusal returns the problem code, and a write needing a person's confirmation refuses until they give it."

Requirement An MCP tool MUST title its action imperatively, describe its behavior declaratively, use positive parameter polarity, and state its side effects.

Rationale The MCP specification carries the title and description to the model. The model plans from them. An imperative title states the action. A declarative description states what happens instead of commanding the caller. The server's guidance and the model's own plan then do not compete. A positive boolean such as paused avoids the inverse polarity that a model answers wrongly. A stated side effect answers the review that asks what the call did.

Example

{
  "name": "pause_webhook_deliveries",
  "description": "Pauses or resumes delivery to one subscription. Events published while paused are dropped, not queued.",
  "input": {
    "type": "object",
    "properties": {
      "paused": { "type": "boolean", "description": "True to pause, false to resume." }
    }
  }
}

Requirement Each tool MUST name the use cases and permissions it reaches.

Rationale A stated scope lets a reviewer tell which product behavior the tool exposes.

Requirement Every tool that writes MUST refuse until the person confirms the write.

Rationale A person approves each write before the model performs it.

Requirement Tool descriptions and logs MUST exclude secrets and personal data from every field they carry.

Rationale Descriptions reach the model, and logs reach operators. Neither needs values that grant access or identify a person.

Requirement The server documentation MUST state how a user installs and updates the server.

Rationale A locally installed server needs a stated path from release to machine.