IMPOSSIBREW

Add to subscription

add_to_subscription

Adds an IMPOSSIBREW beer to every delivery of the customer's subscription. This tool makes no other change. The AI Brewer shows the exact change and makes it only after the customer replies yes. The message goes to the AI Brewer, the same assistant as on impossibrew.co.uk, which checks identity (email plus delivery postcode, or an order number starting EC plus either). message is the customer's own words. The first call has no conversationId; each result returns the conversationId that continues the same conversation across these order tools. The reply is the AI Brewer's complete answer.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "message": "<message>"
    },
    "name": "add_to_subscription"
  }
}

Input Schema

Name	Required	Description	Default
`message`	Yes
`conversationId`	No

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 3, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly=false, destructive=false, idempotent=false, so the safety profile is known. The description adds genuinely useful behavior beyond that: preview-then-confirm, identity verification by email plus postcode or EC order number, conversation threading via conversationId, and that the reply is the assistant's complete answer. It stops short of saying what happens on a failed identity check or whether the add is reversible.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the action and scope, then the no-other-change guarantee, then flow mechanics. A few clauses (the co.uk comparison, the identity detail) are wordier than needed, but nothing is redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema exists, yet the description explains what comes back: the assistant's complete answer and a conversationId to continue with. Combined with the confirmation and identity prerequisites, an agent has everything required to call this mutation correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0%, so the description must carry the parameters and it does: message is "the customer's own words" and conversationId is absent on the first call and returned by each result to continue the conversation. Both of the two parameters are explained with meaning the schema lacks.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource with scope: "Adds an IMPOSSIBREW beer to every delivery of the customer's subscription," plus the constraint "This tool makes no other change." That distinguishes it in substance from skip_next_delivery or cancel_subscription, though it never names a sibling explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a clear usage context: the change is only applied after the customer replies yes, and the first call carries no conversationId. It does not name alternatives for related intents (e.g. basket building or pausing), so the when-not guidance is absent.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All IMPOSSIBREW tools Inspect

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