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Saybooks

by io.github.alviso
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End subscription

purch_end_subscription
Destructive

Record that a subscription ended because the person cancelled it with the vendor, with a reason. Periods after that are no longer expected. Saybooks cancels nothing with the vendor; it only stops expecting the charge. Cancelled is a fact the person states, not something the module infers: a subscription that stops charging shows as lapsed on its own, and stays that way until the person says it was cancelled. Record when, if they know, in the reason. Effects: subscription cancelled.

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": {
      "subscription_id": "<subscription_id>",
      "reason": "<reason>"
    },
    "name": "purch_end_subscription"
  }
}

Input Schema

NameRequiredDescriptionDefault
reasonYesWhy, and when if you know.
subscription_idYesThe subscription, e.g. SUB-0001.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4.3/5.0
Behavior4/5

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

Annotations already flag destructiveHint=true and idempotentHint=false, but the description adds real context beyond them: Saybooks does not cancel anything vendor-side (consistent with openWorldHint=false), and periods after the end date are no longer expected while prior periods are implicitly preserved. What it does not say is whether the action can be reversed or what happens on a second call to an already-cancelled subscription.

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?

Four sentences, front-loaded with the action and effect, and each sentence contributes something (action, non-action, cancelled-vs-lapsed distinction, effect summary). The trailing 'Effects: subscription cancelled' is mild redundancy with the opening sentence.

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

Completeness4/5

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

For a two-parameter destructive mutation with no output schema, the definition covers what is recorded, what is explicitly not done externally, and the downstream consequence on expected periods. The remaining gap is reversibility and error behavior on repeat invocation, which an agent preparing a destructive call would want.

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

Parameters3/5

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

Schema description coverage is 100%, so both parameters are already documented, including 'Why, and when if you know.' The description's line 'Record when, if they know, in the reason' largely restates the schema rather than adding new syntax or format guidance, so the baseline of 3 applies.

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

Purpose5/5

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

States a specific verb and resource: record that a subscription ended because the person cancelled it with the vendor. It also draws a sharp conceptual boundary between 'cancelled' (a stated fact) and 'lapsed' (an inference), which is exactly the distinction an agent needs to pick this tool over doing nothing or misusing a status field.

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

Usage Guidelines5/5

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

Explicitly conditions use on the person stating a cancellation, and explicitly excludes the inverse case: a subscription that merely stops charging shows as lapsed on its own and should not be marked cancelled. The alternative course of action is named in behavioral terms even though no sibling tool is named.

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

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