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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds that portability data is always returned regardless of the `type` selection, which is a useful behavioral note, but it says nothing about auth failures, rate limits, or cost.

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-loaded with purpose and return contents in two tight sentences, then a concrete example call. The example largely duplicates the schema's own example, which is mild redundancy, but nothing is bloated.

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 carries the burden of describing returns, and it does so concretely (carrier, line type, CNAM, portability fields). Only error/permission behavior is unaddressed, which is a minor gap for a 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?

Schema description coverage is 100% – the `type` enum semantics, the E.164 requirement for `phone_number`, and the `_apiKey` origin are all documented in the schema itself. The description merely restates these in prose, adding no syntax or format detail beyond what the schema provides, so baseline 3 applies.

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 ('look up') and precisely enumerates the resources returned: carrier name, line type, CNAM caller name, and portability/LRN details (ported status, LRN, city/state). No sibling tool overlaps this domain, so the definition is unambiguous about what it does.

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?

Usage is implied by the purpose (enrich a phone number), but there is no explicit statement of when to reach for this tool versus other enrichment tools such as entity_profile or company_facts, and no prerequisites beyond the API key. It is adequate but leaves routing to inference.

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