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

No annotations are provided, so the description carries the full burden, and it does substantial work: it discloses that NANP lookups return the most specific exchange/thousands-block record, whether block detail or fallback was used, the common field set, and the meaning of thousands=-1 vs 0-9. It omits any permission, rate-limit, or error behavior, keeping it below a 5.

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 the core purpose and usage cue, then layers output detail. It runs several sentences but each carries distinct information (NANP behavior, field list, thousands semantics), so little is wasted.

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 must supply return-value context, and it does: field list, specificity behavior, fallback indicator, and thousands interpretation. Auth is handled by the api_key parameter, so nothing essential for correct invocation is missing.

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% with both parameters documented, so the baseline is 3. The description adds only implicit meaning for the tn format (dialable number), re-stating rather than extending the schema's own text.

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 (normalize to E.164) and resource (dialable phone number) plus a secondary function (country metadata). Very clear what it does, though it never names a sibling tool to contrast against, so it falls short of full sibling differentiation.

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?

'Prefer this whenever the user gives a full phone number' gives clear when-to-use context. However, no when-not-to-use guidance or named alternatives (e.g. get_exchange, get_exchange_thousands) are given, leaving the boundaries to inference.

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