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

Annotations already declare readOnlyHint=true, and the description is consistent with that by describing simulation rather than mutation. It adds useful behavioral context that annotations don't provide: what metrics get computed, that it samples opening hands, and that it runs mirror self-play. The seed-related reproducibility is left to the schema, so a small gap remains.

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?

Three dense sentences with no filler: the first describes the core behavior and outputs, the second gives routing guidance, and the third states the critical input id rule. It is front-loaded with the verb and resource and every sentence 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?

The tool has no output schema, so the description's enumeration of result metrics (Basics per opener, Trainer density, card show rates, closing speed, first-player bias) tells an agent what to expect. It also covers legality ('legal 20-card deck') and the single-deck vs. two-deck boundary. A minor gap is that the exact return structure is not specified, but the listed metrics are sufficient for correct selection and invocation.

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 description coverage is 100%, so the baseline is 3. The description adds value beyond the schema by clarifying that gameplay card ids are required, not printing ids, which maps directly to the gameplayCardId parameter. It also reinforces the '20-card' constraint from the deck schema, helping agents validate inputs before calling.

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 opens with a specific verb and resource: 'Solo-trial one legal 20-card Pokémon TCG Pocket deck,' then enumerates concrete analyses (opening-hand consistency, mirror self-play, closing speed, first-player bias). It also names a sibling tool to differentiate from, making the purpose unmistakable.

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 states when to use this tool versus its alternative: 'Use this to tune a single deck; use simulate_matchup to compare two decks.' It also provides a crucial prerequisite: 'Takes gameplay card ids, not printing ids,' preventing a likely invocation error.

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