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

Annotations already declare readOnly, idempotent, non-destructive, so safety is covered. The description adds real behavioral context beyond that: precisely which rules are enforced and that pricing is included, which the agent could not infer from the annotations.

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 tight sentences, front-loaded with the validation scope, followed by the input format. No filler, though the parenthetical rule list is slightly dense.

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 should indicate what a validation result looks like (valid/invalid, error listing) or how pricing is returned. It covers inputs and rules well but leaves the response shape unspecified for a tool whose whole purpose is reporting a check result.

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 50% — the 'source' enum is documented in the schema, but 'decklist' has no schema description. The description compensates by specifying the exact line format and giving examples ('4 GD05-019', 'Side Deck' marker), adding substantial meaning for the undocumented parameter.

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 (check/validate) plus the resource (decklist), and enumerates exactly what is validated (50-card main, max 4 copies, 2 colors, banlist, sideboard) in addition to pricing. This clearly separates it from siblings like price_list or save_deck.

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 description effectively tells the agent when the tool applies via the input format and what it validates, but it never names alternatives or exclusions (e.g. use save_deck to persist, price_list for pricing only). Usage is implied rather than stated.

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