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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the bar is lower, and the description still adds real value: no storage or logging of phone numbers or text, no account access, and no message sending. It omits error/failure behavior, which keeps it from a 5.

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?

Three short sentences, front-loaded with what is produced, followed by constraints and privacy notes. Each sentence earns its place; minor redundancy in listing both 'does not store' and 'does not log'.

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 simple link builder with an output schema (so return values need no explanation) and full safety annotations, the description covers purpose, precondition, and privacy. The only shortfall is silent handling of locale/defaultCountry.

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 only 25%, so the description needs to compensate. It covers the phone precondition and the optional message, but leaves 'locale' and 'defaultCountry' completely unexplained in both schema and description — a meaningful gap for a 4-parameter tool.

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 concrete verb and artifact ('Create a wa.me URL') plus the optional prefilled message, which is specific enough that an agent can distinguish it from siblings like format_whatsapp_text or normalize_whatsapp_numbers. It stops short of naming any sibling explicitly, so it falls just below a 5.

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?

'for copying or sharing' implies the use case, and 'Requires a valid phone number; does not verify WhatsApp registration' sets a precondition. There is no explicit when-not guidance and no routing to alternative tools, leaving usage partly inferred.

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