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

The annotations already declare this as a read-only, idempotent, non-destructive operation. The description adds useful behavioral context by explaining that the output is a widget containing balances, plan prices, and Pay/Upgrade buttons, though it does not clarify the exact return format or whether those buttons are purely presentational.

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 two tightly written sentences with no filler. It front-loads what the tool shows and then immediately states when to use it.

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 input parameters and no output schema, the description carries the burden of explaining the returned content and does so by listing the wallet balance, top-up amounts, auto-recharge status, plan prices, and widget buttons. That is sufficient for an agent to understand what invoking this tool will provide.

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 there is no parameter semantics to document. The baseline for a zero-parameter tool is 4, and the description does not introduce unnecessary parameter discussion.

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 and resource: it shows the wallet balance, top-up amounts, auto-recharge status, and all Spur plans with prices. The mention of a widget with Pay/Upgrade buttons gives it a distinct identity relative to sibling billing tools such as get_billing_summary or manage_billing.

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 clear usage triggers: add funds, buy credits, upgrade, change or compare plans, or a failed send for billing reasons. It does not explicitly exclude alternatives or explain when to use sibling tools like spur_top_up_wallet or spur_change_plan instead, so it stops short of full routing guidance.

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