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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely new behavior — result ordering (newest first) and the intended polling loop — but says nothing about what an empty response looks like, whether history is truncated, or any rate limiting on repeated polls.

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?

Two short sentences, zero filler, with the scope and ordering front-loaded before the polling hint. Nothing could be cut without losing information.

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 no-output-schema, single-parameter read tool, the definition covers scope and ordering well enough to call it correctly. The remaining gap is the unresolved relationship with poll_sms and the absence of any note on empty results.

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?

Only one parameter and schema coverage is 100%; the schema itself explains the accepted number format and that '+', spaces and dashes are ignored. The description adds nothing about the parameter, which is acceptable at full schema coverage but is the baseline, not a contribution.

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 (read the SMS a rented number has received) plus the scope 'during this rental' and the ordering 'newest first'. It does not name or differentiate from the sibling poll_sms, which reads as a near-duplicate purpose, so it stops 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?

The only usage instruction is 'poll again every few seconds while waiting for a message', which is a cadence hint rather than a when-to-use rule. With a sibling literally named poll_sms, the agent is given no basis for choosing between the two, and no note on what to do if the rental has expired or the number is not rented.

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