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

Annotations already indicate a read-only, idempotent, non-destructive operation, and the description adds meaningful behavioral context: it is free and non-billable, requires the API key, returns only the caller's own data, and enumerates the exact metrics included (balance, call counts, credits, per-tool breakdown, lifetime spend). This goes well beyond the annotations.

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?

The description is three sentences with no filler, front-loads the core purpose, and packs in the key qualifiers (free, non-billable, own usage only, default window, metric breakdown). Every sentence contributes useful 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 one-parameter, read-only tool with no output schema, the description is sufficiently complete: it names the returned data categories, the look-back window default, and the caller-scoping constraint. An agent can decide whether to call it and understand what it will receive.

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?

With schema description coverage at 100%, the schema already documents the single 'days' parameter including its range and default. The description only repeats the 30-day default without adding new semantic detail, so it meets the baseline but does not elevate 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?

The description states a specific verb ('get') and a clear resource ('API usage & credit balance') and immediately distinguishes it from the sibling data tools by framing it as 'Your own account status' that 'only ever returns your own usage.' This leaves no ambiguity about what the tool returns.

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 clear the tool is for retrieving the caller's own usage and credit balance, and it adds practical guidance by noting it is free, non-billable, and requires an API key. It does not explicitly name alternative tools or state when not to use it, but the sibling pool is obviously different in subject matter, so this is a minor gap.

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