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

With no annotations provided, the description carries the burden of behavioral disclosure. It states 'Read-only, no cost' and 'always works — the receipt lives on-chain', which informs the agent about safety and reliability. It does not mention failure modes or return format details, but for a 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?

Two sentences with zero waste. The first sentence states what is returned, the second explains lookup methods and safety. Critical information is front-loaded and every phrase adds value.

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?

The description lists the returned fields, both lookup methods, and discloses read-only status. With no output schema, this is sufficient for an agent to know what to expect. Minor gaps like precedence when both parameters are provided are not addressed, but the tool's simplicity makes this acceptable.

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 coverage is 100%, so both parameters have descriptions. The description adds value by explaining that payment_ref is the more reliable lookup method and provides an example format for receipt_id. This goes beyond the schema's basic type descriptions.

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 (Fetch) and resource (full receipt details) and enumerates the specific fields returned (digests, checks, outcome, amount, buyer, seller, timestamp, PDA). This clearly distinguishes it from sibling tools issue_receipt and verify_receipt, which focus on creation and verification respectively.

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 provides clear lookup guidance: use receipt_id or x402_payment_ref, and explicitly notes that payment_ref always works because the receipt lives on-chain. It does not explicitly contrast with siblings, but the purpose is distinct and the usage context is well-defined.

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