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

The description adds tremendous value beyond annotations. It defines the three tiers of data confidence (high/medium/low) and provides a critical disclaimer, clarifying that the validation is 'structural' and not proof of active issuance.

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 dense with technical information (e.g., data_version, sources[], time zones), which necessitates a longer format. However, every sentence provides essential technical context rather than repetition.

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 complexity of international telecommunications and identification, the description is complete. It fully outlines the various output formats, derived metadata, and the limitations of the 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?

While the schema coverage is 100%, the description enhances the input semantics by advising when the 'default_region' parameter can be omitted (i.e., when the international format is provided).

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 specifies the function: parsing, validating, and formatting phone numbers. By using this specific functionality, it clearly distinguishes itself from the sibling validation tools (e.g., validate_bic, validate_iban).

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?

It provides an explicit example of input format (number '050 123 4567', default_region 'AE'), guiding users on when certain parameters are necessary. The focus on phone numbers versus other identifiers makes usage context clear.

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