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

It explicitly says 'Read-only,' which duplicates the annotation, but adds that packs are available to 'the project owner' and that eurCents is the identifying field. These details provide scoping and usage context beyond the basic readOnlyHint.

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?

The description is two short sentences, front-loaded with the verb 'List,' and contains no redundancy or filler. Every clause adds value.

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 parameterless list tool with clear purpose and a referenced follow-up action, the description is fully sufficient. No output schema exists, but the simple nature of the tool means the description covers what is needed.

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, so the parameter semantics are trivially satisfied. The description mentions eurCents as an output identifier, which is a useful hint without any formal parameter docs 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 description clearly states it 'List the prepaid credit packs the project owner can purchase,' which is a specific verb+resource. It distinguishes from sibling list tools by focusing on credit packs and referencing start_topup as the follow-up action.

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 description gives practical guidance by saying 'Identify a pack to start_topup by its eurCents,' implying this tool is used to select a pack for purchase. It does not explicitly list alternatives or when-not-to-use, but the context is clear enough.

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