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 safety profile is covered. The description adds only "Returns full meaning structure" plus a cost note that defers to the caller's plan; it does not describe coverage (full 78-card deck?) or response shape beyond that.

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?

Two short sentences, front-loaded with the lookup operation and its example, with no filler. The appended [Group]/[Cost] tags are boilerplate rather than description prose, which slightly dilutes it but costs little.

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 all three parameters are documented in the schema. For a simple read-only lookup the description is nearly sufficient; only card-set coverage and slug-miss behavior are unstated.

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 coverage is 100%, so the baseline is 3, but the description adds real value by giving concrete slug examples ("the-fool", "ace-of-cups") that clarify the lowercase-hyphenated convention better than the schema text alone. The `fields` and `precision` compact-mode parameters are left entirely to the schema.

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 and resource ("Single RWS card lookup by slug") and gives concrete slug examples, so the agent knows exactly what it retrieves. It clearly differs from draw_* or interpret siblings by being a pure lookup, but it never explicitly contrasts itself with the sibling list tool `astroway_tarot_rider_waite_cards`.

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?

Use case is implied by a single-card lookup keyed on slug, and the examples hint that the caller must already know the card. There is no explicit when-to-use/when-not guidance and no routing to alternatives such as the full `cards` listing when the slug is unknown.

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