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

Annotations already denote readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds valuable non-obvious context: these are TEST packs, the operation is a GET, and credits are not granted by checkout alone—this last point cautions against a plausible misuse.

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 brief sentences, each earning its place: the first identifies the resource and endpoint, the second gives the critical lifecycle caveat. No fluff, no repetition of schema or annotations.

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 zero-parameter list tool with readOnly annotations, this is nearly complete: it covers the test nature, the endpoint, and the related checkout/confirm flow. The only minor gap is that the pack types (image ocr, ocr text, vision text) appear in the title but not the description, which could help agents interpret results.

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 has zero parameters and the empty schema is 100% described. With no parameters, the baseline is 4 and the description need not add parameter detail—there is nothing to document.

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 clearly states 'Prepaid TEST packs (GET /credits/packs)', specifying the verb 'list' and the resource 'credit packs'. It also differentiates from sibling write tools by noting the checkout/confirm flow, even though it doesn't explicitly name an alternative read 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 lifecycle note ('checkout_credits is intent only; credits grant after confirm_credits') implies this is the read-only step before checkout/confirm, giving useful context. However, it doesn't explicitly state when to use this tool versus alternatives, such as 'list packs before initiating checkout'.

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