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

Beyond the readOnlyHint annotation, the description discloses important behavioral nuances: that bans changed multiple times in 2026, that the commander parameter counts toward the deck count, and that omitting commander results in a response saying color identity went unchecked. These details help the agent understand the tool's behavior and limitations.

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?

The description is a single, focused paragraph that opens with the core purpose, then adds a persuasive justification for using the tool, and finishes with parameter specifics. Every sentence earns its place; it is concise without being sparse.

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?

For a validation tool with an output schema, the description covers the essential context: what rules are checked, why it's needed, and how to handle Commander. It also explains a common failure mode (unchecked color identity). The presence of an output schema reduces the need to describe return values, making this description complete.

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?

The description provides detailed semantics for the commander parameter, explaining its role and impact. However, it does not elaborate on the format parameter (e.g., allowed values) or the cards array structure beyond what the schema already shows. With 0% schema description coverage, the description only partially compensates, leaving these parameters under-specified.

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 clearly states the tool validates a decklist against constructed format rules, specifying exactly what it checks (banned cards, deck size, copy limits, and color identity in Commander). It uses a specific verb and resource, and the purpose is distinct from sibling tools like rate_deck or deck_stats.

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 explicitly instructs to use this tool rather than recalling ban lists from memory, citing a concrete reason (frequent ban changes and stale training data). It also provides conditional guidance for the commander parameter, explaining when to pass it and why it's necessary for color-identity checking.

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