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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, but the description adds genuinely new behavioral context: which price sources are returned, that d90Pct can be null for CardTrader until history exists, that Cardmarket d30Pct is null until ~late October 2026, and that spoiler:true cards are pre-release and may change. That freshness/caveat detail is real value beyond the structured fields.

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?

Single sentence, front-loaded with the core purpose ('Full details for one card'), with the dense parentheticals carrying genuinely useful null/percentage semantics. Slightly overloaded but every clause earns its place.

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 no output schema, the description carries the full burden of describing the return payload — stats, effect text, keywords, rulings, every printing with multi-currency prices and change metrics, plus tournament usage — and it does so thoroughly, including null caveats.

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?

Only one parameter with 100% schema coverage; the schema already documents the cardNumber format (GD01-001) and the description adds no extra format syntax. Baseline 3 is appropriate when the schema does the work.

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 (get) and resource (full details for one card), and the 'one card' scope implicitly distinguishes it from the sibling search_cards list operation. An agent knows this is single-card detail retrieval, not discovery.

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: fetch this when you already have a cardNumber and want everything about that card. It never names the alternative (search_cards) or states when-not to use it, and there is no prerequisite guidance. Adequate but leaves routing to inference.

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