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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world behavior. The description adds useful context: it returns a Call link and the person talks in the browser, and crucially 'this tool does not dial.' It does not cover pricing source or currency, but those are not strictly required.

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?

Front-loads what the tool returns and when to use it, then gives parameter format, then a key behavioral caveat. Sentences are purposeful, though the E.164 detail duplicates the schema.

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 explains the return values (price per minute and Call link) and the non-dialing behavior. It is sufficient for calling correctly, though it does not differentiate from the sibling country-price tool.

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 100% and the single parameter already includes E.164 format and an example. The description repeats the same E.164 format instruction and example, adding no semantics beyond the schema.

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: returns price per minute and a Call link for a phone number. It clearly describes the output and that it does not dial, but does not explicitly distinguish itself from the sibling get_country_call_prices.

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?

Provides clear when-to-use guidance: 'Use it when the person wants to call a phone number or asks what a call to it costs.' It does not mention alternatives or exclusions, such as when to use the sibling country-level tool instead.

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