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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, yet the description still adds a genuinely non-redundant behavioral fact: 'Costs nothing', i.e. the call does not consume quota. It also discloses the payload's shape (plan, count, refill time) despite there being no output schema. It does not describe response format details or whether the count resets on a rolling vs. fixed window.

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 short sentences, front-loaded with what is returned and then when to call it. There is mild redundancy between 'today's count' and 'what is left today', which keeps it from being maximally tight.

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 zero-parameter, no-output-schema utility, the description supplies purpose, return content, cost, and invocation timing – enough to call it correctly. Remaining gaps (refill window semantics, exact response shape) are minor.

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?

The tool takes zero parameters, which is the baseline-4 case; there is nothing for the description to clarify. It correctly avoids inventing parameter behavior that does not 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 names the concrete return payload – the plan, today's count, and the refill timing – so an agent knows exactly what resource this exposes. It does not need to distinguish itself from the astrology siblings, which are an entirely different domain. It stops short of a clean verb+resource statement ('usage'), but the substance is unambiguous.

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 two explicit trigger conditions: after a call fails on the limit, and proactively before a long series of calls. No alternative tool exists for this purpose, so there is nothing left to disambiguate.

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