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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safe-read profile is covered without description help. The description adds content conventions (deck size, trump numbering, pip interpretation) that are useful interpretation context but not behavioral traits such as pagination, rate limits, or return shape — and with an output schema present, the return format need not be repeated here.

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?

Three tight sentences, front-loaded with the highest-value fact (78-card Marseille deck) and the numbering caveat that most affects interpretation. The trailing [Group:]/[Cost:] tags are boilerplate metadata rather than description prose, so the size is well judged.

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 annotations covering safety, a full output schema covering the return payload, and 100% parameter documentation, the description only needs to establish scope and tradition — which it does via the 78-card count and Justice/Strength swap note. Only the lack of explicit sibling differentiation keeps it from being fully complete.

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%, so the baseline is 3. The two parameters (fields, precision) are generic compact-mode controls that the description does not touch at all; it neither clarifies nor obscures them, and the schema already carries the semantics.

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 precisely (the full 78-card Marseille deck) and adds distinguishing interpretive conventions — Justice=8, Strength=11, pip minors read by number+suit — which separate it from the Rider-Waite lineage. It never explicitly contrasts with nearby siblings like astroway_tarot_marseille_majors or astroway_tarot_marseille_cards_slug, so the agent must infer scope from '78-card' alone.

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?

Usage is only implied: stating '78-card' signals a full-deck reference lookup as opposed to the majors-only or slug-lookup siblings, but there is no explicit 'use this when' or named alternative. The agent can infer intent, but nothing routes it away from cards_slug if slug-keyed access was actually wanted.

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