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

Annotations already declare readOnlyHint/idempotentHint and the description reinforces this with 'Nothing changes.' Beyond that, it adds genuinely useful behavioral context not in the annotations: the remaining amount is 'a portion, not the ceiling' and the output may include a pending budget request and a stored-card flag. It stops short of describing format or freshness of the data.

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?

It is one dense enumerating sentence followed by two short directive/behavioral sentences, so the critical 'what you get' content is front-loaded. The enumeration is long but each clause maps to a distinct output field, so the length largely earns its place.

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 and no parameters, the description must carry the whole burden of communicating return values, and it does: it walks through mode, currency, per-currency remaining budgets, seller caps, pending requests, thresholds, and card storage. An agent knows exactly what it will learn and why to call it.

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, which per the rubric sets the baseline at 4. There is no parameter surface for the description to clarify further, so it cannot score higher on this dimension.

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 names the specific resource (this agent's own spending situation) and enumerates its scope in detail: sandbox/live mode, home currency, per-currency budgets and remaining amounts, seller caps, pending request, approval threshold, stored card. This is far more specific than a status tool that shares the budget/approval space, letting an agent distinguish it from siblings like budget_request_status and approval_status.

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?

It gives explicit trigger conditions — 'Call it before shopping or when a purchase was refused' — and states the goal (explain and pick the right currency or seller). It does not, however, explicitly rule out or name the sibling tools (budget_request_status, approval_status) that an agent might otherwise reach for.

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