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

Annotations only indicate readOnlyHint=false and openWorldHint=false, so the description carries the burden of explaining side effects. It does well by disclosing the one-time on-chain settlement and that subsequent calls are debited off-chain. The phrase 'Price: Free' is slightly ambiguous because buying credit obviously costs USDC, but it likely means the tool itself has no service fee.

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 concise and front-loaded with the core action, then gives the trigger condition and a useful cost heuristic. Every sentence contributes actionable information, with no filler or repetition of the schema.

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 single-parameter tool with no required inputs and no output schema, the description is complete. It covers what the tool does, when to use it, the payment mechanism, billing behavior, and cost expectations. An agent has enough context to decide whether to call it and what to expect.

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?

Schema description coverage is 100%, so the input schema fully documents amount_usd with its allowed values and default. The description doesn't add further parameter-level detail, but it doesn't need to; the baseline of 3 applies.

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 ('Buy'), a concrete resource ('Kortex credit'), and the payment method ('USDC on Base over x402'). This clearly distinguishes it from the listed sibling tools, none of which involve purchasing credit. Even the title 'Top up balance' reinforces the purpose.

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 explicitly says when to use: 'Call when your balance is low.' It also provides helpful context that operations are cheap, so one deposit covers many operations. It doesn't explicitly mention when not to use it or compare it to an alternative, because no sibling is a natural alternative, so no exclusion is needed.

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