validate_phone

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

No annotations provided, so description carries full burden. It clarifies what 'valid' means (conforms to numbering plan, not live line) and mentions output formats. However, it does not explicitly state read-only or side-effect status, though implied by validation purpose.

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?

Three sentences with no waste. The first sentence front-loads the core instruction and purpose. Every sentence adds essential information without redundancy.

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?

For a 2-parameter tool with no output schema and no annotations, the description provides purpose, usage guidelines, meaning of validity, and output return types. It is sufficient for an agent to use the tool correctly without additional context.

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 coverage is 100% with descriptions for both parameters. The description adds important context beyond schema: it emphasizes the region parameter's critical role in correctness and explains that 'number' is the phone number. This adds value over the schema alone.

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 validates and normalizes phone numbers to E.164 format, using specific verbs 'check' and 'normalise'. It distinguishes from sibling validation tools by being phone-specific, and the 'USE THIS' imperative clarifies its domain.

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 explicitly says 'USE THIS to check...' and gives a mandatory guideline: 'You MUST pass the ISO country the number ACTUALLY belongs to.' It also clarifies the prerequisite for region and warns against reusing unrelated country fields.

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