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

With no annotations available, the description carries the full behavioral disclosure burden. It reveals only that the tool works offline, but says nothing about input validation, error handling, or behavior with malformed numbers. These gaps are significant for an unannotated tool.

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 sentence with no filler; every phrase names a specific output format or the offline constraint. It is efficiently front-loaded, though it sacrifices completeness for brevity.

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 simple one-parameter tool, the description misses critical context: the meaning of q, acceptable input format, and how to choose this tool among many phone-related siblings. The output schema may cover return values, but input and selection context remain incomplete.

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?

The schema has one parameter 'q' with zero description, and the tool description does not define what q should contain. While one can infer q is a phone number, its expected format (e.g., country code, separators) is absent. With 0% schema coverage, the description fails to compensate.

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 identifies the tool as a phone number formatter producing E.164, national, international, and RFC3966 formats. This is a specific verb+resource that differentiates it from other phone-related tools by its formatting focus. It could be more explicit about being only a formatter, but the purpose is unambiguous.

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 provided on when to select phonefmt over sibling tools like phone, phonevcard, phonepivot, or phonecc. The 'offline' note offers a minimal selection hint, but there are no explicit when/when-not conditions or comparisons to alternatives.

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