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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds value beyond them: the concrete endpoint, plan availability, per-call cost in request units, that the payload is Turkish JSON, and that it carries `source` and `guncelleme` metadata. It also warns that the carrier reported may be the original rather than the current one, which is a real interpretive caveat.

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?

Front-loaded with the return payload, then a compact operational block covering endpoint, cost and response shape. Dense comma-separated enumerations ('E.164 / international / national', '0850, 444, toll-free…') are efficient for a Turkish-context audience, though the opening sentence is long and carries a lot at once.

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, so the description must carry the return contract — and it does, listing every field an agent would need to reason about the response, plus the Turkish-language and metadata caveats. For a two-parameter read-only lookup, nothing material is left unspecified.

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%, and the schema already documents `numara` formats and `ulke` as an ISO 3166 alpha-2 defaulting to 'TR'. The description adds no syntax or defaulting detail beyond that, so the schema does the work here and baseline 3 applies.

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 opens with a specific verb and resource ('Parses a phone number') and then enumerates exactly what comes back: validity, country, line type, E.164/international/national formats, province, original carrier and masked form. That enumeration distinguishes it cleanly from validation siblings like iban_dogrula and dogrula_vergi_no, which handle different identifiers.

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 gives practical selection context — available on all plans including free, costs 1 request unit per call — which tells an agent this is a cheap, unrestricted call worth making freely. What's missing is explicit routing guidance: it never names a sibling or states a when-not condition, though the narrow subject matter makes misuse unlikely.

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