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

With no annotations, the description carries the full burden and discloses nothing: not whether it is a read-only list, whether it requires auth, or what it returns (a catalog of packs with prices and sizes?). The fragment is behaviorally empty.

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?

It is short, but shortness here reflects under-specification rather than economy. The single fragment is not front-loaded with actionable information and contains no sentence that tells the agent anything useful.

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 catalog tool with no output schema and no annotations, the description must at least imply the shape of the result and the calling context. It does neither, leaving the agent to guess whether this is a list endpoint, a purchase flow, or metadata.

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 there is nothing for the description to explain; baseline 4 applies. No parameter semantics are missing.

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?

"Purchasable credit packs" restates the tool name as a noun phrase without a verb or any indication of what the tool does with them (list? fetch? create?). An agent cannot distinguish it from siblings credits_checkout_url or credits_history on the basis of this text.

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, when-not-to-use, or alternative named. Nothing tells the agent whether this should be called before credits_checkout_url or credits_history, or under what circumstances.

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