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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful non-annotation context: WhatsApp sends must use an approved template, and the payload is exactly the JSON body of POST /api/v1/messages. It stops short of describing delivery failures, rate limits, or idempotency.

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 tightly packed sentences, front-loaded with the capability, then the payload contract, then the safety instruction. No filler or restatement of the title.

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?

No output schema exists, so return values are undocumented, but the description covers the platform variants, payload contract, recipient sourcing and the confirmation requirement, which is most of what an agent needs. Absence of error/response behavior is the remaining gap.

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 0%, so the description carries the burden, and it does add meaning: the single `message` param is the exact POST /api/v1/messages body, and `recipient` is a platform-scoped sender id (an E.164 phone number on WhatsApp). This clarifies field semantics the schema only encodes structurally via oneOf/patterns, though it does not explain accountId vs profileId.

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 (send) plus resource (direct message) and enumerates the exact platform variants: Instagram/Facebook text DMs and approved WhatsApp templates from the profile's own number. That scope distinguishes it cleanly from siblings like create_post, reply_to_comment and list_messages.

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 concrete operating context: recipient comes from list_messages, and it instructs the agent to confirm the text with the user before sending. It does not, however, state when to prefer this over reply_to_comment or what to do if the platform/account combination is unsupported.

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