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

readOnlyHint already declares the tool is read-only; the description adds non-obvious context: the call is free, it returns specific bands and resource keys, and the same price map drives x402 payments and the x-price-usd header. This meaningfully exceeds what annotations alone provide.

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?

The description is longer than minimal but front-loads the purpose and then adds a justification, return shape, subscription caveat, and consistency guarantee. The wallet metaphor is vivid and reinforces the urgency, though it could be trimmed without losing meaning.

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 properly explains what will be returned: cost bands, priced resource keys, and the map underlying payment headers. It also covers when prices are included in plans. Nothing essential is missing for an optional-parameter read-only lookup.

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 only parameter, context, is already fully documented in the schema with 100% coverage. The description does not add parameter-specific guidance, but none is needed because the schema carries the explanatory burden completely.

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 first sentence states exactly what the tool returns: per-call cost bands on the pay-as-you-go plan. It goes further by enumerating the bands and noting that every priced resource key is included, so the resource and scope are unmistakable and distinct from sibling get_* tools.

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 description explicitly says to call this BEFORE budgeting a run of paid tools and explains why it is free. It also clarifies subscription coverage, but it does not name an alternative tool or state when not to use it; the guidance is still clear and actionable.

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