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

With no annotations provided, the description must carry the full behavioral burden. It does well by disclosing key behaviors: balance is counted in DELIVERIES, not money, and packs never expire. This is non-obvious and critical for proper use. The only minor gap is not describing the return structure or error cases, but for a zero-parameter read-only tool, this is adequate.

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 three sentences, each adding value. It front-loads the core purpose, then provides key behavioral context, and ends with a clear call-to-action. No filler or redundant phrasing. This is a model of conciseness.

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 tool with no output schema, the description is remarkably complete. It covers what the tool does, key behavioral quirks, and when to use it. An agent can confidently call this tool without further clarification. The only minor omission is the exact response format, but given the simplicity, this is not a 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, and schema coverage is 100% (vacuously). The description adds substantial meaning by clarifying that the tool requires no input and returns pricing info. It compensates for the lack of parameters by explaining what the tool returns, which is exactly what an agent needs.

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 clearly states the tool's purpose: to provide delivery costs, pack types, and x402 payment requirements. It distinguishes itself from sibling tools by focusing on pricing/payment, which is unique among the listed siblings (most are task/destination operations).

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 explicitly instructs when to use this tool: 'Call this before buying.' This is a direct usage guideline. It also indirectly suggests that this is the pricing tool, and since no sibling tool has a similar pricing focus, it implicitly establishes itself as the go-to for cost queries.

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