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

The description adds 'No authentication required', a behavioral trait not present in the annotations, and clarifies the billing model. Since annotations already declare readOnlyHint and idempotentHint, the description supplements them with a useful operational detail. There is no contradiction between the description and 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?

The description is a single 12-word sentence with every clause carrying meaning: the resource, the conversion factor, and authentication requirement. It is appropriately front-loaded with the core purpose and contains no redundancy or filler.

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 tool with an output schema, this description is complete. It covers the purpose, the critical credit-to-envelopes relationship, and the authentication requirement, leaving no gap for an agent to call it correctly. The output schema handles return-value details, so no further explanation 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 and the input schema covers everything, so the description has no obligation to explain parameter meanings. The baseline for zero-parameter tools is 4, and the description does not need to add anything here. Its note about authentication is behavioral, not parameter-related.

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 identifies the resource, credit packs and billing model, and the defining conversion factor (1 credit = 1 envelope send), making it clear that this tool returns pricing information. It lacks an explicit action verb, but the tool name 'get_pricing' provides the verb, and the content differentiates it from buy_credits and check_balance.

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 provides context that implies usage, such as the credit-to-envelope conversion and 'No authentication required', which indicates this is a low-stakes informational call. However, it does not explicitly state when to choose this over buy_credits or check_balance, nor does it name any alternatives or exclusions. Usage must be inferred from the tool name and sibling names.

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