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

Annotations already establish readOnly, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description still adds genuinely new facts beyond them: zero token cost and the presence of an actionable top-up link in the response, both of which affect agent planning.

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, front-loaded with the resource ('this account's plan'), that spends every clause on a distinct return value. No filler, no 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?

With no output schema present, the description carries the burden of describing returns and does so by enumerating each field of the payload plus the conditional top-up link. For a parameterless, read-only status tool this is fully sufficient to call it correctly.

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?

Zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The description correctly focuses its words on outputs instead of inventing parameter behavior.

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?

Names a specific resource (this account) and enumerates exactly what is reported: plan, remaining Casafari tokens, credits expiring within 30 days, current call eligibility, and a top-up link. None of the sibling tools (all claro_* search/plot tools) overlap with this, so the agent can distinguish it at a glance.

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 closing note 'Free (uses no tokens)' gives an explicit cost-based decision rule and the 'whether calls can be made now' clause implies the diagnostic use case (check before or after hitting limits). It stops short of stating when to call it relative to other operations (e.g. on quota errors), so it is clear context rather than full when/when-not guidance.

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