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

Annotations already provide readOnlyHint=true and idempotentHint=true, so the safety profile is known. The description adds valuable context beyond annotations: the warning about spoofing of incoming calls, the data source (numertel.pl), and the return fields (source link, verification date). No contradiction.

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 well-structured with clear sections: purpose, usage, returns, and a security warning. Each sentence earns its place, though the use of all-caps emphasis is slightly noisy and could be toned down. It is efficient but not maximally concise.

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?

All essential contextual aspects are covered: what it does, when to use it, what it returns (verified numbers with source link and verification date), and a critical security caveat about spoofing. The output schema exists, so return details are handled. Low complexity (one parameter) makes this description complete.

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 100%, so the baseline is 3. The description reinforces examples of institution names (ZUS, mBank, PKO, NFZ) but does not add new semantic details beyond the schema's parameter description.

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 finds the REAL, official phone number for banks, offices, or operators in Poland, and can also verify if a number in a message is the official hotline. It uses a specific verb ('Znajdź') and resource, and is distinct from siblings like check_phone_number which likely checks scam numbers.

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 'UŻYJ, gdy użytkownik pyta...' and lists concrete use cases (e.g., asking for official number or verifying a provided number). However, it does not mention when not to use the tool or alternatives, so it misses the 'when-not' and 'alternatives' part for a 5.

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