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

Annotations already establish readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: the call is free, the price map is the same one used by x402 payments and the x-price-usd header so all three agree, and prices only apply to per-call access. It does not describe a response shape, but the free/consistency guarantees are substantive.

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?

Purpose and the FREE/call-first instruction are front-loaded. The 'already been refused by its own wallet' line is rhetorical flourish rather than operational content, but the rest is dense with useful detail and not padded.

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 carries the return-value burden and does so adequately: it lists the cost bands and states that every priced resource key is included. An agent has enough to call this correctly and interpret the result.

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?

Schema coverage is 100% for the single optional 'context' parameter, so the schema already documents it. The description never mentions the parameter or how it is used (read only if a result is wrong), adding nothing beyond what the schema states.

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+resource ('what one call costs ... by cost band') and enumerates exactly what is returned (the bands and every priced resource key). No sibling tool covers pricing, so it is trivially distinguishable from the find_/get_ catalog 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?

Gives an explicit when: 'Call this BEFORE budgeting a run of paid tools,' and clarifies that subscription plans include these calls. It does not name a competing tool or a when-not condition, but the timing guidance is unambiguous.

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