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

Far exceeds the annotations (which only say destructive/openWorld/non-idempotent): it explains the pre-send name/language check against the number's templates, the specific 422 error codes, the fact that the check accepts unapproved templates, and the conditions under which the check is skipped entirely (unreadable Meta templates, >100 templates), yielding a 202 whose verdict appears in status. This is exactly the kind of behavioral nuance the annotations cannot carry.

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?

Purpose is front-loaded in the first sentence, followed by increasingly detailed caveats. Every sentence conveys substance (approval requirement, check behavior, failure modes), though the dense multi-clause sentences around the >100-template edge case read as slightly run-on.

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 complex, side-effecting tool with no output schema, the description covers the safety-critical behavior thoroughly: approval prerequisites, validation semantics, async 202 outcomes, and where the failure status surfaces. It stops short of stating what the immediate response returns (e.g. a message id), which would complete the picture.

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 75% and the nested schema is extremely detailed (headers, buttons, media limits, OTP aliases), so the schema carries the parameter burden. The description adds no per-parameter meaning of its own, so the 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?

The opening sentence states a specific verb (send) and resource (Meta-approved WhatsApp template), making the operation unambiguous. It does not name or contrast the sibling send_whatsapp_message / send_conversation_message, so an agent must infer that this is the template-only path, which keeps it just short of 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?

Gives real context: templates can be sent at any time, including outside the 24-hour customer-service window, and points to listWhatsAppTemplates for status and required fields. It never explicitly says when to prefer this over the free-form send siblings, so the routing guidance is useful but incomplete.

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