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

Annotations already declare readOnlyHint=false, destructiveHint=false, and idempotentHint=false, so the agent knows this mutates auth state. The description usefully adds that a session_token is issued and that first_name is conditionally required for shared numbers, but says nothing about code expiry, retry behavior, or failure modes.

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, zero filler, with the core action and return value front-loaded and the conditional parameter caveat appended last.

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?

For a 3-parameter auth-completion tool with full schema coverage and no output schema, the description covers the action, the returned token, and the conditional parameter. It could add a word on code validity/expiry, but nothing essential is missing.

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 baseline is 3, but the description adds rationale the schema lacks: first_name is needed specifically when multiple people share the phone number, versus the schema's terse "Solo se richiesto". This meaningfully clarifies when to supply the optional 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+resource ("Completa l'accesso con il codice WhatsApp") and notes the return value (session_token). The verb "completa" implicitly pairs with the sibling start_login as the second step, though it never names that sibling explicitly.

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 implies this is the step following the one that produced request_id, and it states the condition for supplying first_name (shared phone number). It does not explicitly contrast with start_login or say what to do if the code is invalid/expired.

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