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

The description reveals that the tool calls the external Loqate service, requires an API key, and returns specific data fields (confidence, number type, carrier, recommendation). This adds valuable context beyond the readOnlyHint and openWorldHint annotations, covering auth needs and external dependency. No contradictions with annotations.

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?

The description is two sentences long, with the core purpose and output in the first sentence and the key requirement in the second. It is front-loaded, direct, and contains no superfluous information.

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?

Given the complete parameter schema, present annotations, and absence of an output schema, the description adequately covers the essential context: purpose, return values, and the API key prerequisite. It could be more complete by mentioning potential error cases or policy defaults, but those are already in the schema. Overall, it provides sufficient information for correct invocation.

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%, so each parameter already has a clear description. The tool description only mentions the 'key' field explicitly, which is already documented in the schema. It does not add additional meaning or clarify parameter usage beyond what the schema provides, so a baseline score of 3 is appropriate.

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?

The description clearly states the tool's action and scope: 'Verify a phone number via Loqate.' This distinguishes it from sibling verification tools (verify_address, verify_email, etc.) by specifying the resource type. It also summarizes the key output components, leaving no ambiguity about purpose.

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?

The description provides clear context for when to use the tool: whenever phone number verification is needed. It does not explicitly name alternatives or exclusions, but the resource-specific language ('Verify a phone number') inherently guides selection. The API key requirement is also stated, which is a practical usage prerequisite.

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