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

With no annotations, the description carries the full burden and does reasonably well: it discloses the return fields (validity, normalized number, area code, city) and the per-call cost/currency, which an agent needs for cost-aware planning. It stops short of describing failure behavior for malformed input.

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?

Four short sentences, each earning its place: purpose, worked example, use case, return contract, then pricing last. Purpose is front-loaded and nothing is repeated from the schema.

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?

There is no output schema, and the description compensates by spelling out the four return fields. Parameter documentation is complete and the tool is simple, so the only remaining gap is error/precondition behavior for invalid numbers.

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%, so the baseline is 3; the description adds slight semantic value by implying the area code (e.g., 021 for Tehran) should be part of the value, clarifying how to shape input beyond the schema's 'any common format'.

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?

States specific verbs (validate, normalize, resolve) on a specific resource (Iranian landline number + area code). The landline scope implicitly separates it from the sibling validators (fa_validateMobile, fa_validatePostalCode, etc.) without the agent needing to open another schema.

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?

Gives concrete when-to-use cases: verifying a fixed-line contact or routing a support request by region. It does not name alternatives or state exclusions (e.g., when to prefer fa_validateMobile), so it falls short of the top mark.

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