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

With no annotations provided, the description carries the full burden of behavioral disclosure. It merely says 'Validate phone number' without explaining accepted formats, the role of default_region, return value structure, or any validation rules. This offers minimal transparency about how the tool behaves.

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 a single short sentence with no wasted words, which is efficient. However, it is so under-specified that conciseness borders on insufficiency, though it still achieves a clear purpose statement.

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 tool's simple in/out nature, a one-line description might seem adequate, but the presence of a default_region parameter, sibling validator tools, and no output schema or annotations leaves the description incomplete. It does not explain how the result is returned or how region affects validation.

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%, and the description does not mention either parameter. The agent gets no additional meaning beyond the raw schema fields ('phone' and 'default_region'), leaving the tool's parameters semantically opaque.

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 function with a specific verb and resource ('Validate phone number'). While it is unambiguous and distinguishes itself from sibling validators by targeting phone numbers, it provides no additional detail about scope or format, so it just misses a 5.

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?

No guidance is given on when to use this tool versus alternatives like extract_phones or validate_email. The description is a bare statement of purpose with no context about suitability, prerequisites, or exclusion criteria.

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