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

Annotations already declare readOnly, idempotent, non-destructive and non-open-world, so the safety profile is covered. The description adds genuinely new behavior: results reflect what is sold "today" (freshness) and that purchasing is deliberately out of scope, routed to another tool. Return shape and any staleness/caching detail are the only gaps.

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 sentences, zero filler. The read-only nature and the handoff to the purchase tool are front-loaded immediately after what the tool returns, so the most decision-relevant facts come first.

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 carries the burden of describing return values, and it does so concretely: price, billing interval, inclusions. Combined with the explicit read-only/purchase boundary, an agent has everything needed to call this correctly.

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 sets the baseline at 4. The description correctly implies a no-argument call by scoping the result to the catalog as it stands today, with nothing to explain away.

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 gives a specific verb and resource ("List the plans GYSM sells") and enumerates the payload (price, billing interval, what's included). It also draws a clean boundary against the purchase flow, so an agent can tell this apart from checkout-oriented siblings.

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?

It states the context explicitly: read-only browsing here, buying via subscribe_to_gysm with a Stripe link. That is a clear alternative-plus-condition. It stops short of a full 5 because subscribe_to_gysm does not appear in the supplied sibling set (start_checkout does), and no guidance distinguishes this from plan-comparison siblings like compare_ai_app_builders.

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