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

Annotations already declare readOnlyHint=true and destructiveHint=false. The description adds useful behavioral context beyond that: the packs are TEST-only, the operation is a GET, and actual credits are only granted after confirm_credits. No contradiction with annotations.

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 short sentences, front-loaded with the core purpose and endpoint. The second sentence earns its place by clarifying that checkout_credits alone does not grant credits, which helps an agent avoid a common misuse. No filler or repetition.

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, read-only listing tool with no output schema, the description covers the essential information: resource, test nature, endpoint, and surrounding credit flow. It does not describe what a credit pack contains or whether the list is paginated, but that burden is low for such a simple 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?

The input schema has zero parameters, so the baseline is 4. There is nothing to document beyond what the schema already shows; the endpoint mention is sufficient and no parameter-level detail is needed.

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 title and description clearly state the operation: listing credit packs. The description adds specificity with 'Prepaid TEST packs' and the explicit GET endpoint (/credits/packs), so the resource and scope are unambiguous. It also references checkout_credits and confirm_credits, which helps an agent place this tool within the broader credit-purchase flow.

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?

There is no explicit guidance on when to use list_credit_packs versus alternatives such as credit_balance or quote_credits. The sentence about checkout_credits being intent-only clarifies a related flow but does not tell the agent when choosing this tool is appropriate or inappropriate.

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