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

Annotations already declare the safety profile (readOnly, idempotent, not destructive, closed-world), so the bar is lower. The description earns credit for adding the concrete endpoint and an honest cost disclosure ('not in the public credit manifest'), which flags real billing uncertainty that annotations do not cover. It stops short of 5 because pagination/error behavior on an unknown slug is unstated.

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-line purpose sentence is front-loaded, followed by a bracketed metadata block that is scannable and zero-waste. Slightly telegraphic rather than fully prose, but no filler sentences.

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?

An output schema exists, so return values need not be explained, and annotations fully cover the read-only/idempotent profile. Endpoint, group and cost are supplied. The only real omission is how to discover a valid slug, which is a minor gap for a lookup-by-key tool in a rich structured context.

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 all three parameters (slug, fields, precision) are documented in the schema itself, including the compact-mode syntax and precision bounds. The description adds nothing beyond repeating 'Required: slug', 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+resource+scope: 'Single Marseille card lookup by slug'. The word 'Single' implicitly contrasts with the sibling list tool astroway_tarot_marseille_cards, so an agent can distinguish it, but the sibling is never named explicitly, so it stops short of a clean 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?

The description gives no when-to-use guidance and never points at alternatives. It never says that astroway_tarot_marseille_cards is how you obtain a valid slug, nor when the majors/spreads siblings would be preferable. 'Required: slug' restates schema metadata rather than giving usage direction.

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