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

Beyond readOnlyHint=true, the description discloses pricing ('Free'), error behavior for unknown/unsettled ids (RECEIPT_NOT_FOUND), and a retention window (30 days after settlement). These are substantive operational facts an agent cannot get from the annotations or schema.

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?

Three short sentences, front-loaded with the purpose, followed by cost, error case, and retention. No sentence is redundant and nothing is buried.

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 an output schema present, return values need no explanation, and the annotations cover safety. The description still covers cost, failure mode, and data lifetime, leaving no material gap for an agent calling this single-param read tool.

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% and the schema already documents the 'rcpt_' + 64 hex format, so the baseline is 3. The description adds semantic constraint by implying the id must belong to a settled paid call, which goes slightly beyond the schema's format-only documentation.

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 opens with a specific verb+resource: 'Re-fetch the stored result of a settled paid call by its receipt_id.' This is unambiguous and an agent can immediately tell what the tool returns and what it operates on, even though the sibling tools are unrelated.

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 states the triggering condition clearly ('for when the response was lost after payment'), which is exactly the scenario that should select this tool. It also implicitly scopes usage to settled calls via the RECEIPT_NOT_FOUND note, though it names no alternative tools for other recovery paths.

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