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

Annotations already declare destructiveHint=true, so the description does not need to re-state that sending a message is a side effect. It adds useful behavioral context by requiring recipient verification and that whatsapp_user_id be a provider identity, but does not elaborate on consequences like irreversibility or sending limits.

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 deliver the action, the prerequisite, and an identity constraint with no filler. The key scoping detail ('new 1-to-1 chat') is front-loaded, and each sentence earns its place.

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?

Given the schema covers all parameters, annotations convey destructive behavior, and the description adds the essential recipient-resolution workflow and provider-identity constraint, the definition is complete for an agent to select and invoke the tool correctly. No output schema is present, so return-value details are not required.

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 schema describes each parameter, but the description adds critical meaning by clarifying that whatsapp_user_id must be a provider identity, never a display name, and that recipient resolution must come first. This goes beyond the bare schema definition.

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?

The description states a specific action ('Start a new 1-to-1 WhatsApp chat and send the first message') and clearly identifies the resource. It differentiates from related messaging tools by emphasizing 'new' chat and first message, signaling this is not for continuing an existing conversation.

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?

It provides clear context on when to use the tool by instructing the agent to resolve/verify the recipient first with whatsapp_list_contacts or a profile/number lookup. It does not explicitly name an alternative like whatsapp_send_message for existing chats, but the 'new' framing implies the distinction.

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