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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorldHint=false, so the safety profile is covered. The description's one genuine contribution is disclosing that the response may include candidate rows when the receipt is unmatched — helpful return-shape context, though it says nothing about how matching state is determined or what a candidate row contains.

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?

One short, front-loaded sentence with no filler. Its brevity is efficient rather than padded, though the missing verb costs a little readability.

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 no output schema, the description is the only source of return-value information, and it provides just the headline (receipt plus conditional candidate rows). That is enough to orient an agent but leaves the receipt's own fields and candidate structure unexplained.

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?

A single required receipt_id with full schema description coverage, so the schema does the work and a baseline 3 applies. The description adds no information about the identifier format or what happens if it is unknown.

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?

"One receipt and, if unmatched, its candidate rows" identifies the resource (a single receipt) and hints at the return shape, but the verb is elided and the name alone carries most of the meaning. It is distinguishable from purch_receipts (plural list) only by the near-identical naming convention, not by anything the description says.

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?

No when-to-use or when-not guidance is given. An agent must infer that this is the single-record fetch relative to purch_receipts, and nothing points to the related purch_match_receipt / purch_unmatch_receipt actions that consume the candidate rows mentioned here.

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