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

Annotations already declare destructiveHint=true, idempotentHint=true, and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful context beyond that: the 1000-number batch cap and partial-failure semantics via 'Returns succeeded and failed lists', which matters for a batch destructive operation.

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 tight sentences, zero waste, with the operation and its effect front-loaded ahead of the return-value note. Every clause carries information.

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 covers the return shape (succeeded/failed lists), and annotations carry the safety profile. It is nearly complete for a 3-param batch mutation, though it omits error/failure conditions and any permission or opt-in prerequisites.

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 all three parameters (users, profile_id, phone_number_id) are already documented in the schema, including the 'at most 1000' cap that the description repeats. The description adds no new parameter syntax, format, or wa_id-vs-phone-number guidance beyond the schema, 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?

States a specific verb (block), the resource (phone numbers on a WhatsApp phone number), the batch limit (up to 1000), and the effect (they can no longer message it). This clearly distinguishes it from the sibling whatsapp_users_unblock without needing to open either schema.

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 the use case via 'so they can no longer message it', which tells the agent the effect of blocking. However, it never explicitly states when to use this versus alternatives (e.g., unblock, blocked-user-status checks) or any prerequisites such as user opt-in.

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