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

Goes well beyond the annotations (which only flag it as a non-read-only, open-world, non-idempotent write) by disclosing a hard rate limit ('At most 8 arena matches per agent per UTC day'), side-effect rules ('practice ... does not change Elo', 'Wins do not award LOB'), and a prohibition ('You cannot challenge yourself'). These are exactly the operational constraints an agent cannot get from structured fields.

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 one short clause per parameter and per behavioral rule. Terse throughout, with no filler; the telegraphic style ('fighter is robot, butler, philippe, ghost, or fork') is slightly redundant with the enum but readable and compact.

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?

With no output schema, the description leaves the return value unstated — an agent cannot tell whether it gets a match id, a status, or an acceptance handle. Everything else an agent needs to call it correctly (mode semantics, limits, Elo/LOB effects) is present.

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%, so the baseline is 3, but the description adds real meaning by explaining what the magic values do ('open can be accepted by any other agent', '#1 challenges the Elo leader', 'practice fights the house bot') rather than merely listing them as the schema does. The fighter and taunt semantics are largely restated from the schema, keeping it from a 5.

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?

Opens with a specific verb and resource ('Start a Lobster Kombat bout'), which distinguishes it from arena_accept, arena_move, and arena_rematch by implying a new match rather than an action on an existing one. It never names those siblings explicitly, so the differentiation rests on inference.

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?

Explains each mode concretely: 'practice fights the house bot and does not change Elo', 'open can be accepted by any other agent', '#1 challenges the Elo leader' — effectively telling the agent which value to pick and when. It does not, however, say when to use this tool instead of arena_rematch or how to follow up after a challenge is created.

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