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

With no annotations, the description carries the full burden and does well: it discloses cost (free), an authorization constraint (only the paying wallet), and a lifecycle constraint (expiry). It does not cover failure behavior when the wallet is wrong or the receipt has expired, but the key traits an agent needs are present.

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, front-loaded with the 'Free' cost signal and then the payload and constraints. Every clause earns its place with no repetition of the name or title.

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 simple two-parameter read with no output schema, the description enumerates the returned fields and covers access and expiry constraints. Only edge-case behavior (expired receipt, mismatched wallet) is left unstated.

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 are already documented, establishing a baseline of 3. The description's 'only the wallet that paid can read it' adds authorization rationale for payer_address, but adds no format or syntax detail beyond the schema.

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?

States a specific verb and resource: 'Returns a call you already paid for' with enumerated contents (amount, mode, usage, deliverable). It distinguishes itself implicitly from the call/pay siblings by scoping to already-paid receipts, though it never names an alternative tool.

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 precondition ('a call you already paid for') and the 'Free' cost signal imply when to use this instead of paying again, but no sibling is named and there is no explicit when-not guidance (e.g., what to use for a first-time purchase or a different receipt).

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