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

Beyond the destructiveHint=true annotation, the description discloses the non-obvious side effect that pending reminders are cancelled and rescheduled when status, next_charge_date, reminder_offset_days, or notice_period_days change, and it fully specifies the two-step confirmation protocol. It still does not say whether omitted fields are left untouched (patch vs. replace) or what happens on an invalid id, which matters for a destructive mutation.

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

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

Three dense sentences, front-loaded with purpose, then side effects, then the confirmation contract. The field list is long but functional; nothing is padding, though the CONFIRMATION block could be tightened slightly.

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

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

For a destructive 12-parameter mutation with no output schema, the description covers scope, editable surface, reminder side effects, and the propose/confirm return contract. The remaining gap is update semantics for omitted fields and failure behavior, which an agent would want before calling.

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

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

With 0% schema description coverage across 12 parameters, the description carries the load and does so by naming every editable field and attaching behavioral meaning to several of them (status values cancel reminders; date/offset/notice changes reschedule). It does not explain the intent of parameters like notes, cancel_url, or category, and defers formats and bounds entirely to the schema.

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

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

States a specific verb and resource ('Update one of the caller's subscriptions by id') and immediately enumerates the editable fields, which separates it from add_subscription, delete_subscription, and get_subscription without needing to name them. The ownership scope ('Only the caller's own subscription is reachable') further pins down what this tool can act on.

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

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

Routes the agent explicitly: this tool only proposes the write, and the actual mutation happens via confirm_action after the caller supplies the action_id and plan_token. That names the alternative and the condition under which it is used, leaving no ambiguity about which sibling to call next.

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