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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds meaningful semantic guardrails: it does not authorize or execute a purchase and makes no model-cost savings claim. This goes beyond the structured annotations without contradicting them.

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?

A single, front-loaded, information-dense sentence with no filler. It states what the tool is, what it exposes, and what it does not do, all in an efficient format.

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 catalog, the description provides enough context about contents and non-purchase behavior. It does not define the exact return shape, but since there is no output schema, this is a minor gap; 'prepaid packs and billing principles' indicates the subject matter well.

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 no parameters, so there is no parameter burden on the description. It clearly describes the catalog content, which is sufficient for a zero-argument tool.

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?

Description names a specific resource ('commercial catalog for the managed Mithrandir service') and a specific action ('Shows prepaid packs and billing principles'). It also disambiguates from sibling tools by explicitly stating it does not authorize or execute a purchase.

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 a clear use case—retrieving pricing/pack/billing information—and an explicit exclusion: it is not for purchasing. However, it does not name sibling alternatives such as mithrandir_quote or mithrandir_onboarding_pay, so an agent must infer which other tool handles purchase execution.

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