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

Annotations already declare readOnlyHint=false, openWorldHint=true, idempotentHint=false, and destructiveHint=false, so the safety profile is covered. The description adds genuinely new context: the key is bound to exactly one number and cannot message anyone else, and replies arrive out-of-band via get_replies. It does not mention rate limits, cost, or delivery failure behavior, which keeps it short of a 5.

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?

The core mechanic and its constraint lead, followed by usage triggers, authoring advice, and the reply path. Every sentence carries information the agent needs; nothing is restated from the schema verbatim.

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 single-parameter, no-output-schema tool, the definition covers purpose, the one-number binding constraint, when to invoke, how to phrase the message, and how to retrieve the answer. No meaningful gap remains for an agent deciding whether and how to call it.

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%, so the 160/1600-character guidance is already documented, and the baseline would be 3. The description earns an extra point by explaining the absence of a recipient parameter, which the schema cannot convey since it only lists properties that exist.

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 precise verb and resource ('Send a text message to the phone number that owns this SelfPing API key') and immediately distinguishes itself from its only sibling by explaining that replies are read through get_replies. An agent can identify the tool's scope without opening the schema.

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 gives concrete trigger conditions ('when a long job finishes, a deploy completes, or an error fires') and explicitly routes the read path to get_replies. The 'no recipient argument' clause also tells the agent not to attempt any other recipient, which is an exclusion no schema can express.

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