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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely new context: the call is free, requires no API key, and returns per-call unit costs plus which capabilities work unauthenticated. It could go slightly further on result size or caching, but the auth and cost model is well disclosed.

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?

Return contents are front-loaded, followed by cost/no-key behavior and then usage triggers. The first sentence is a dense run-on list of fields, but every clause carries information an agent needs; nothing is filler.

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?

There is no output schema, so the description must describe the return payload, and it does so field by field (prices, units, limits, features, checkout_url). Combined with the auth disclosure and invocation triggers, an agent has everything needed to call and interpret it.

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, so there is nothing to disambiguate and the baseline of 4 applies. The description correctly implies a single unfiltered catalog response rather than a parameterized query.

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 resource (plans and prices) and enumerates exactly what comes back: monthly price, included units, limits, features, checkout_url. An agent can distinguish it from get_subscription or get_usage immediately, since those are about the account rather than the catalog.

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?

Explicit triggers are given: before a large batch, when a human asks about cost, or before create_checkout_link. It also supplies a negative rule ('never quote prices from memory') and names the dependent sibling (create_checkout_link), leaving nothing to inference.

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