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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds one genuinely useful piece of non-annotation context: the cost note ('see your plan — endpoint not in the public credit manifest'). It says nothing about pagination or payload shape, though the output schema exists.

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?

One front-loaded sentence followed by two compact metadata lines; nothing is padded. The bracketed group/cost lines are boilerplate but short and informative.

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?

With full annotations, a complete input schema and an output schema, the safety and return-shape burdens are carried elsewhere. The remaining gap is routing guidance versus the sibling card-listing tool, which the description does not close.

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?

Schema description coverage is 100% and every parameter (slug, fields, precision) is already documented with format hints in the schema. The description adds no syntax or format detail beyond that, so the baseline 3 is correct.

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?

States a specific verb (lookup), a specific resource (single Marseille card) and the key (slug), which is enough to separate it from the plural sibling astroway_tarot_marseille_cards. It does not explicitly name that sibling, so it stops short of a 5.

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 when-to-use guidance and no alternative is named. The contrast with astroway_tarot_marseille_cards is only implicit in the word 'Single', leaving the agent to infer when a card-by-slug lookup is preferable to listing cards.

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