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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the bar is lower, yet the description still adds real value: it discloses that replies are link-only, that no price is embedded, and that mutations must happen on the site. The 'Under 30 tokens' cost note is a useful behavioral signal not present in structured fields.

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?

Labeled Purpose/When/Cost sections make it front-loaded and scannable at roughly 45 words. Minor slack from the slightly overlapping 'no price is stated here' clause, which restates the pricing-link point rather than adding new information.

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 parameters, rich annotations, and an output schema that covers the return shape, the description supplies everything an agent needs: what comes back (two links), when to call it, and that it costs almost nothing. 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?

The tool takes zero parameters, so the baseline of 4 applies; there is nothing for the description to disambiguate beyond what the empty schema already conveys.

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 concrete resource (the two subscription site pages: pricing and the billing-portal account page) and clarifies scope by noting 'no price is stated here,' which functionally separates it from subscription_get. It falls short of a 5 only because it never names subscription_get as the sibling the agent should prefer for plan/price data.

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?

'When: The user wants to see prices, subscribe, change or cancel' gives explicit triggering intent, and 'changes happen on the site, not in this assistant' pre-empts misuse for actual mutations. There is clear routing context but no named alternative tool for the price-lookup case.

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