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

Annotations already cover read-only/idempotent/non-destructive, but the description adds genuinely new behavior: valuation timing ('marked at the pools' price now'), the play-money framing, a cost ('Costs 1 unit'), and an auth failure mode ('refused without a key'). This is context the structured fields cannot supply.

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 and dense with no filler, but the deeply nested return-field inventory is long and makes the block heavier than strictly necessary even though no output schema exists to carry it.

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 carries the return contract itself — naming top-level fields (name, profile, cashUsd, totals) and the shape of open[]/closed[] entries including nested band fields — so an agent knows exactly what it will receive.

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?

Zero parameters, so the baseline is 4 and no compensation is needed. The description's field enumeration describes the response, not inputs, which is appropriate given there are none.

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+resource: 'Reads the caller's own arena account.' The possessive scope ('own') and the explicit contrast with arena_standings ('for everyone's ranking') let an agent distinguish it from the sibling without opening either schema.

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?

Gives a concrete trigger ('before arena_open or arena_edit') plus an explicit alternative for a different need (arena_standings). Nothing about when to reach for this vs. neighbours is left to inference.

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