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

Annotations already declare destructiveHint=true, idempotentHint=true, and openWorldHint=true, so the safety profile is covered. Beyond that, the description adds real behavioral value: the price points ($29/month vs $290/year) and the carve-out that pre-10 October 2026 subscriptions retain their price and yield a 409 legacy_plan. It still omits what actually happens on switch (proration, effective date).

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?

Two front-loaded sentences with no filler. The second sentence is terse to the point of being cryptic, however: "keeps its price (409 legacy_plan)" packs a price-lock rule and an error code into a parenthetical without explaining the relationship.

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 two-parameter mutation with no output schema, the description covers purpose, pricing, and one important edge case, which is adequate. It leaves gaps an agent would care about: whether the switch takes effect immediately, what happens to in-flight billing, and what a successful or failed call returns.

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?

Schema description coverage is 50%: order_id is documented with its source (my_orders), but `to` is only an enum with no prose. The description compensates partially by describing the two states and their prices, but never maps them to the `to` parameter or explains how order_id is validated.

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?

The description names a specific verb (Switches) and a specific resource and scope (the Monthly drive's billing period for one product), with concrete prices distinguishing the two target states. An agent can distinguish it from cancel_monthly or drive_stop, though the tool's internal term "drive" is never reconciled with the clearer title.

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?

Usage is implied rather than stated: it's clear this is for toggling an existing subscription's billing period, and the order_id lookup path (from my_orders) is supplied by the schema. There is no explicit when-to-use versus cancel_monthly, drive_stop, or followup_drive, and no stated preconditions such as required account state.

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