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

Annotations already confirm readOnly/idempotent/non-destructive, so the description wisely spends its words elsewhere: no API key required, the values are caller-supplied blended rates rather than platform quotes, and no call is placed. It omits any note on output shape or precision, but the added context is genuinely useful.

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 short sentences, no filler, with the pricing scope front-loaded and the disclaimers trailing. Every clause earns its place.

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?

For a simple three-parameter, read-only calculator with annotation coverage, the description is nearly sufficient; the caller understands inputs, currency, and that results are estimates. It could note the output components explicitly since there is no output schema, but this is a minor gap.

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 description coverage is 0%, so the description must carry the load. It clarifies that provider and carrier rates are caller-supplied and denominated in USD, which adds real meaning, but it says nothing about the required `seconds` parameter or per-minute rate basis beyond what property names already suggest.

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: calculate USD platform fees plus caller-supplied provider/carrier rates. The closing 'Does not place a call' separates it from the call-creation siblings without needing to name them.

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?

'Public, no key' and 'an estimate, not a provider quote' imply a pre-commitment costing use case, but the description never routes to alternatives such as get_provider_matrix or get_billing_policy for authoritative rates. Usage is inferable rather than stated.

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