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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), so the description's job is to add behavior beyond that — and it does: a non-exact name does not fail but returns close matches to choose from. It also enumerates what the result contains. It omits any statement about error behavior for ambiguous ids or result limits, keeping it below the top mark.

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 sentences with no filler; the returned-field list is front-loaded and the input/fallback behavior follows. The phrasing 'what ArcaneMetriX reads in it' is slightly oblique compared to a plain 'also returns role and tags,' but nothing is wasted.

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?

There is no output schema, so the description carries the burden of describing results, and it does so by enumerating the card fields plus role and tags. Combined with the documented fuzzy-match fallback and the annotation-covered safety profile, an agent has what it needs to call and interpret this tool, with only minor gaps (no indication of return structure or failure modes).

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?

With a single parameter at 100% schema coverage the baseline would be 3, but the description adds real semantics the schema lacks: the field accepts either a card name or a Scryfall oracle id, and a non-exact name triggers a fuzzy-match response. That directly shapes how the agent should call the tool and how to interpret the result.

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 names the resource precisely (a Magic card's identity: mana cost, type, color identity, legalities, image) plus the derived fields (deck role, tags) and states the accepted input forms. It is clearly a lookup of a single card rather than a deck-level or synergy analysis, though it never explicitly contrasts itself with card_synergy or suggest_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?

Usage is only implied: the agent can infer this is the tool for resolving a card by name or oracle id before doing anything else. There is no explicit when-to-use or when-not-to-use statement and no named alternative for related tasks like synergy, so guidance is adequate but thin.

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