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

Annotations already establish readOnly/idempotent/non-destructive/closed-world, so the bar is lower. The description adds genuine value beyond them: the tool is free, it is scoped strictly to the caller's own data ('only ever returns your own usage'), and it explains the two consumption models (plan-based vs. prepaid API credit) and the look-back window. It stops short of describing return structure or freshness, so not 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?

Three tight sentences, front-loaded with the core purpose and scoping statement. Dense with facts and no filler, though the API-key clause is slightly compressed and could be marginally clearer with a touch more structure.

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, the description carries the return-value burden and does so fully by enumerating what the caller gets back for both signed-in and API-key modes. Combined with annotations covering the safety profile and a fully documented parameter, nothing needed to invoke it correctly is missing.

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% and the single 'days' parameter is already documented in the schema with its default (30) and bounds. The description restates the look-back window and default but adds no syntax or behavior beyond that, so baseline 3 applies.

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+resource ('Your own account status') and enumerates exactly what it returns: plan, tool calls used vs. plan limit, queryable domains, and for API-key users the prepaid balance and per-tool call/credit consumption. Clearly distinguishes itself from the brand-analysis siblings, none of which touch account state.

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 description makes the use case unmistakable (check plan, quota, and domain access) and notes it is 'Free; only ever returns your own usage,' which signals when it is appropriate. No explicit when-not or named alternative is given, but no sibling tool serves this purpose, so the guidance is effectively complete.

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