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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered; the description adds the valuable detail that scope is bound to the calling API key (no parameters to target another account). It does not say whether the call itself consumes credits or whether rate-limit values are static quotas vs. remaining budget, which is the one behavior an agent would still want.

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 sentences, front-loaded with the return contents, followed by the practical use case. The enumerated fields are all substantive and none of the wording is redundant with 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, the description carries the burden of describing return values, and it does so by listing the five categories of data returned. It does not describe the response's shape or units beyond parenthetical notes on rate limits, so an agent knows what is available but not exactly how it will be structured.

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, so the baseline is 4. The description correctly reinforces that identity is implicit in the API key rather than supplied as an argument, leaving no ambiguity about how to invoke it.

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 verb-and-resource combination ('Returns the calling API key's account info and current usage') and enumerates the exact contents (plan tier, rate limits, credits used/left, enabled scopes). No sibling tool covers account or credit state, so an agent can immediately tell this apart from the company/LEI/sanctions lookups.

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?

Provides a concrete usage scenario in the user's own words ('how many credits do I have left?'), which is exactly the trigger an agent needs. It stops short of stating when-not to call it or naming alternatives, but there is no plausible competing sibling for this purpose.

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