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

Adds substantial behavior beyond the annotations: the 24-hour window constraint on free_form, the requirement that a template carry an approved call_permission_request component, and that the answer arrives asynchronously via whatsapp.call_permission.updated rather than as a return value. Missing are failure behavior when the window is closed and whether re-requesting is allowed. The annotations declare destructiveHint=false, consistent with a request that does not place a call, though openWorldHint=false sits slightly awkwardly against messaging an external contact.

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 sentences and every one carries load; the prerequisite statement is front-loaded before the mode trade-off. The middle sentence is dense with parentheticals but is the most decision-relevant content, so nothing is wasted.

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 tool with six parameters, a nested template object, and no output schema, the description covers the essential unknowns: prerequisite ordering, mode selection, window constraint, and how the result is delivered. The template object's internal shape is left entirely to the schema, which is acceptable given full schema coverage.

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 six parameters are already documented, including the mode-conditional requirements for text and template. The description restates the mode semantics rather than adding new parameter meaning, so the baseline of 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 and resource ("Ask a WhatsApp contact for permission to call them") plus its role as a prerequisite before placing a call. This clearly separates it from get_whatsapp_call_permission (read), send_whatsapp_message (generic message), and place_call, so an agent can pick it without inspecting schemas.

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?

Gives explicit context: it is required before calling, and the two modes have distinct applicability — free_form only inside the 24-hour customer service window, template usable any time. That effectively tells the agent how to choose a mode. It stops short of naming the alternative tool for checking an existing permission status (get_whatsapp_call_permission) or saying when to skip the request.

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