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

Annotations already declare idempotentHint=true and destructiveHint=false; the description adds useful behavioral context by mentioning the skull icon and that defeated combatants skip their turn. No contradiction with 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 short sentences with the main action first and a when-to-use clause second. No filler or redundancy.

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 simple boolean setter with full schema coverage and idempotency annotation, the description plus schema fully covers what the tool does, when to use it, and how the optional combatId behaves. An output schema is not essential for this mutation.

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 100%, with descriptions for combatantId, defeated, and optional combatId including the active-combat fallback. The description does not add parameter-specific meaning beyond the schema, so baseline 3 applies.

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 ('Mark') and resource ('combatant') and adds observable outcomes (skull icon, skipped turn), making it distinct from sibling combat-set-initiative, combat-set-turn, and combat-toggle-combatant-visibility.

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?

Explicitly gives a trigger condition: 'Use when creature reaches 0 HP or is otherwise eliminated.' It doesn't name alternatives or exclusions, but the context is clear enough for selecting among combat siblings.

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