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

Annotations already flag destructiveHint=true and idempotentHint=true, and the description adds substantial context beyond them: timing of the new limits/credits (immediate), timing of the price change (next renewal), the no-refund policy for the current period, and the required billing:write scope. This is exactly the behavioral detail an agent needs before 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?

Front-loads the action, then packs the billing consequences, direction constraint, permission requirement, and confirmation gate into tight clauses. No filler; every sentence carries information an agent must act on.

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?

With no output schema, the description fully covers the preconditions, side effects, and billing timing an agent needs to call a destructive mutation safely. Nothing material is missing.

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 coverage is 100%, so both parameters are already documented, and the description largely restates the tier semantics. It does add a meaningful constraint beyond the schema ('explicit lower tier' — the target must be downward), but it does not enrich the 'confirm' flag beyond what the schema already says.

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+resource (move the subscription down a tier) with immediate scoping of what 'down' means, clearly distinguishing it from upgrade_subscription, cancel_subscription, and pause_subscription in the sibling set. An agent knows exactly what the tool does without opening the schema.

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?

Provides clear when-to-use context ('strictly downward only', 'only call after the user explicitly confirms') and a prerequisite ('requires billing:write'). It does not explicitly name upgrade_subscription as the alternative for upward moves, relying on inference, so it falls just short of 5.

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