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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuine value by previewing the returned payload (community verdict, report counts, business registration, evidence link), which tells the agent what it will learn without opening the output schema. It stops short of stating behavior for a missing or unknown number.

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?

Two sentences, front-loaded with the action and the payoff, no filler. Minor redundancy: the second sentence about the id restates the schema's parameter description almost word for word, so it earns only partial credit.

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?

With an output schema present, the description needn't detail return values, and it still usefully summarizes them; annotations carry the safety profile. The one gap left for an agent is edge-case behavior (unknown number, missing entry), which neither description nor annotations address.

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% and the single `id` parameter is documented in-schema with the same E.164-digits phrasing. The description essentially repeats that constraint verbatim rather than adding new meaning (no format examples, no note on what an invalid id yields). Baseline 3 for a schema-covered parameter.

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 a specific verb ('Retrieve') and resource ('who is behind a phone number from the Calmido directory'), then enumerates exactly what comes back: verdict, report count, top category, registered business, evidence link. An agent can distinguish this from the sibling `search` because the description frames this as the follow-up lookup for a known id.

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 clause 'The id is the one `search` returned' establishes the intended usage sequence: search first, then fetch. What's missing is any routing against the other sibling, `lookup_phone_number`, which is presumably a competing way to resolve a number — the agent gets no signal on when to pick this over that.

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