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

The annotations already establish readOnlyHint=true, openWorldHint=false, and destructiveHint=false. The description adds useful behavioral context beyond that: it identifies the account as signed-in and notes that it picks up top-ups paid since the last check, which helps the agent understand freshness and scope. It stops short of explaining whether the 'last check' marker is updated, so the read-only implication remains slightly ambiguous but not contradicted.

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 primary outputs and followed by a relevant freshness detail. Every phrase contributes; there is no wasted wording.

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 zero-parameter, read-only account tool with no output schema, the description sufficiently explains what is returned: account identity, credit balance, recent credit activity, and newly paid top-ups. It could say more about the exact return shape, but the tool is simple enough that this is not a major gap.

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 has zero parameters, so the description has no parameter semantics to add. Per the zero-parameter baseline, a 4 is appropriate; the schema covers the empty input completely.

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 uses a specific verb ('Show') and names the resources: signed-in account, credit balance, recent credit activity, and top-ups since the last check. This is clear, though the title/name 'whoami' alone would be vague and the description does not explicitly differentiate from nearby payment-related siblings like get_payments.

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 implies usage by saying it shows account and balance information, but it gives no explicit when-to-use guidance, no exclusions, and no alternatives such as get_payments or get_topup_link for payment-specific needs.

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