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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=true), yet the description still adds real value: it declares the tool is free, takes no parameters, hits a live external endpoint, and explicitly is not a purchase — preempting the obvious billing concern. It doesn't mention rate limits or auth, which keeps it below a 5.

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 endpoint, then the return payload, then the no-param/no-purchase guarantees. No filler and nothing repeated twice.

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 carries the return-value burden and does so concretely (row id, paid route, price, fields and CSV). The absence of any auth or rate-limit context for an open-world external call is the remaining gap, but for a free, parameterless sample endpoint it is close to complete.

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 takes zero parameters, so the baseline is 4. The description correctly states "It takes no parameters," which is redundant with the empty schema but harmless and confirms the constraint.

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 ("Calls GET /v1/sample on the Receipts API") and enumerates exactly what comes back: row id, paid route, price, fields and CSV. It implies this is a preview rather than a paid fetch, but never names receipts_index or receipts_pricing, so sibling differentiation is left to inference.

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?

"Free" and "not a purchase" tell the agent this is a no-cost preview, which is useful implied guidance, but there is no explicit statement of when to choose this over receipts_index or receipts_pricing. The usage is inferable rather than stated.

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