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

Annotations already declare readOnlyHint=false, openWorldHint=false, idempotentHint=false, destructiveHint=false, so the safety profile is covered. The description adds useful commercial context (14-day trial, Paystack billing), but says nothing about what invoking it does — whether it starts a checkout, returns a link, or requires an authenticated business account.

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?

A single front-loaded sentence with no filler; the core action and the tier come first and the qualifying audience follows. The phrase 'Show a ... button' is slightly UI-centric and could mislead about the return value, but nothing is wasted.

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 zero parameters and no output schema, the description carries the burden of explaining the result of the call, and it does not. Trial length and payment provider are given, but an agent still cannot predict what comes back or what prerequisites exist.

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?

The tool takes zero parameters, which is the baseline-4 case; there is no argument meaning to explain. The description correctly implies the subscription tier and billing provider are fixed rather than parameterized, which is consistent with the empty 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?

The description names a concrete verb and object ('Show a Start free trial button') scoped to the Business subscription, which lets an agent separate it from get_subscription and manage_subscription. It stops short of saying what the tool actually produces (a URL, a checkout session, or a UI flag), so the action is clear but the outcome is not.

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?

The parenthetical '(for people registering businesses for clients)' implies the audience and therefore an implied when-to-use condition. There is no explicit exclusion or named alternative (e.g. 'use manage_subscription to change an existing plan'), so an agent must infer the boundary.

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