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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely new behavioral facts: the call is free, any key works regardless of scope, and the rate_limit figures are aggregate-across-keys versus per-key. With no output schema, the enumerated return fields carry real weight.

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?

Front-loaded with the one-line purpose and cost/safety claim before the return inventory, which is the right order. The structured bullet list is efficient, though the discount line packs nested parenthetical definitions (rate, threshold_usd, gap_usd) that read more densely than the rest.

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?

No output schema exists, and the description fully compensates by naming every returned field group and its sub-fields, including nested structures like bonus_expiring and per-key vs aggregate usage. An agent knows exactly what it will receive without a trial call.

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?

There are zero parameters, so the baseline is 4 and no semantic burden exists. The description correctly avoids inventing inputs and instead concentrates on outputs.

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: 'Read the account behind this API key', and immediately scopes it ('Free, read-only, any key works'). The bulleted return inventory further separates it from siblings like everyinfra_call_api or everyinfra_get_job, which are action/result oriented rather than account-state oriented.

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?

'Check the balance before a batch of paid calls' gives a concrete trigger for invocation, and 'every paid call's billing also carries balance_after_usd' explains the relationship to paid usage. It stops short of naming explicit alternatives or when-not-to-use conditions, so it lands at 4 rather than 5.

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