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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds only a vague, non-actionable credit caveat and says nothing about match limits, empty results, or how many of the 78 cards may be returned.

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 sentence that earns its place, followed by two clearly delimited metadata tags. No wasted prose; the cost line is uninformative but brief.

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-value explanation is not required. Still, for a search tool the description leaves open behavior that matters to invocation (match volume, ordering, empty-result handling) and gives no when-to-use 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 the keyword parameter's schema text already reads 'Substring match across both upright and reversed keywords', which the description merely echoes. No extra meaning (case sensitivity, ranking, partial-word behavior) is added, so 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 operation (substring search), the resource (upright and reversed keywords) and the scope (all 78 cards). An agent can distinguish it from astroway_tarot_rider_waite_cards or _cards_slug, which retrieve cards by identity rather than by keyword — though the description never names those siblings explicitly.

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 only guidance is a cost note ('see your plan — endpoint not in the public credit manifest'), which is not actionable. There is no statement of when to prefer this keyword-search tool over the sibling card-listing, suit, number, or element lookups.

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