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

Beyond the annotations (readOnlyHint=true, openWorldHint=false), the description adds key behavioral details: 'Returns at most 100 owned cards per call, with the full match count in `total`' and 'Requires a free API key (send it as "X-API-Key: <key>" or "Authorization: Bearer <key>")'. This is valuable context that annotations alone do not provide. No contradiction is present.

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 three sentences long, front-loaded with the core purpose, and every sentence earns its place—scope, alternative, result limits, and authentication. There is no fluff or repetition.

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?

The description covers ownership scope, search criteria, the primary use case, return limits, count behavior, and authentication. Since an output schema exists, the return structure is already documented. The tool is a straightforward search; all necessary context is present in a concise and complete manner.

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 input schema has no descriptions (0% coverage), so the description must compensate. It explains the meanings of colors, types, and notInDecks explicitly, but leaves `query` and `limit` to inference. The 'at most 100' limit is mentioned but not tied to the `limit` parameter. Overall, it adds significant meaning to the key parameters despite not covering all five.

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's specific function: 'Search only the cards the user OWNS' and lists search criteria (name, colors, type). It also distinguishes from sibling search_cards ('Use search_cards instead to search every Magic card regardless of ownership'), so there is no ambiguity about its unique purpose.

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?

Explicit guidance is provided: 'Use search_cards instead' for global searches, and the notInDecks parameter is explained with a concrete use case ('what is sitting idle in my binder'). This tells the agent exactly when to use this tool and when to choose an alternative.

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