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

Annotations already declare read-only, idempotent, non-destructive behavior, so the description adds context beyond that: mutations must happen on the site, not through the assistant, and no pricing data flows back. The explicit token-cost note is genuinely useful for agent budgeting.

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?

Three labelled lines (Purpose / When / Cost) with zero filler and the most decision-relevant information front-loaded. Every sentence carries distinct 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?

An output schema exists, so return values needn't be explained, yet the description still characterizes the two links returned, which helps the agent narrate results. Between annotations, output schema and description, an agent has everything needed to call it 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 no parameters, so there is nothing to disambiguate and the baseline is 4. The description appropriately spends no space on arguments.

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 and resource — returning two site pages (pricing and the account page that opens the billing portal) — and is concrete enough to distinguish it from subscription_get, which would carry plan details. It also explicitly narrows scope with 'no price is stated here.'

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 'When:' line gives clear triggering intents (see prices, subscribe, change, cancel). It does not name a sibling alternative such as subscription_get for plan details, so routing between the two is left partly to inference.

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