play_card

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

With no annotations, the description carries the full burden. It discloses one genuinely useful behavior – 're-resolves the hand index' – warning that previously read indices may be stale. However, it says nothing about energy cost, what happens if the card is unplayable or the target index is out of range, or whether the play is reversible.

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?

Front-loaded with the core action, then a compact Args block that mirrors the two parameters without padding. The parenthetical about hand-index re-resolution is the only non-obvious content and it earns its place; the rest is terse and readable.

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?

An output schema exists, so return values need no explanation, and both parameters are fully documented despite zero schema coverage. For an unannotated mutation tool the remaining gap is failure/validity behavior (illegal card, insufficient energy, invalid target), which leaves it just short of 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?

Schema description coverage is 0%, so the description must compensate, and it does: it names the source of `card_id` (the `id` field from state/decision_pack), gives a concrete example ('Strike_R'), and explains `target_index` as a 0-based enemy index with an explicit omit condition. Only valid ranges and error behavior for bad indices are left unstated.

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 and resource ('Play a card by its `id` from hand') and clarifies the index is re-resolved, so the agent knows exactly what the operation does. It does not, however, distinguish itself from ambiguous siblings like `choose`, `confirm`, or `send_command`, which could plausibly be routes to the same action.

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 implied rather than stated: the agent infers it should call this when it wants to play a card, and the note about omitting `target_index` for non-targeted cards is a useful conditional. There is no explicit when-to-use versus `choose`/`send_command`, and no prerequisite guidance such as needing a pending decision.

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