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

Annotations already declare readOnlyHint=false, idempotentHint=false and destructiveHint=false, so the safety profile is covered. The description adds one genuinely useful behavioral fact beyond them – that a session_token is returned for account tools – but says nothing about single-use codes, failure/retry behaviour, or expiry, which matter for a non-idempotent mutation.

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 short sentences with zero padding: the action is front-loaded and the return value follows. Nothing is repeated and nothing needs to be trimmed.

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 no output schema, the description correctly compensates by naming the returned session_token and its purpose. For a two-parameter, fully-documented tool this is nearly complete; only the flow prerequisite (a prior start_registration call) is left implicit.

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 both parameters (code, request_id) are already documented in the schema with their formats and provenance. The description's "codice WhatsApp" overlaps the schema's "Codice di 6 cifre ricevuto via WhatsApp" without adding new meaning, so 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?

"Completa la registrazione con il codice WhatsApp" states a specific verb (complete) and resource (registration), and pairs naturally with the sibling start_registration. It is clear what the tool does, but it never explicitly differentiates itself from start_registration or complete_login, so an agent must infer the pairing from the name alone.

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?

Usage is only implied: the name and "completa" suggest this is the second step of a flow begun by start_registration, and the schema's request_id text ("restituito dal passo precedente") reinforces it. However the description itself states no when-to-use condition, no prerequisite, and names no alternative, so the agent has to reconstruct the flow.

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