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

With no annotations, the description itself must carry behavioral disclosure. The verb 'Checks' suggests a read-only capability lookup, and the agent-profile scope is clear; however, it does not disclose the return value shape, whether the check is synchronous, or any operational side effects.

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?

A single sentence states the operation, scope, and messaging channels with no redundant wording. Every word 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?

For a simple three-parameter check the description is mostly complete, but there is no output schema and no explicit description of what the tool returns (boolean, capability list, etc.). An agent would still know the intent but may have to infer the exact response format.

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 the schema already documents all three parameters well. The description reinforces that 'recipient' and 'agent profile' matter but adds no new parameter-level meaning beyond the schema.

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 uses a specific verb ('Checks whether') and resource ('recipient's phone number... capable of receiving rich messages') and names the exact scope ('RCS or WhatsApp on a specified agent profile'). This clearly distinguishes it from send_message and other siblings.

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 purpose implies that the tool should be run before sending rich messages to a recipient, but the description does not explicitly say when to use it versus alternatives or when not to use it. Sibling tools like send_message are not referenced.

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