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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds genuinely new behavioral facts: it is free with no payment required, it returns descriptors only and no prices, and it gives the HTTP equivalent (GET /eligible). It does not mention result size, ordering, or pagination.

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 short, but the 'Free:' opener and the later 'Free — no payment required' repeat the same point, and the em-dash chain packing eligibility criteria plus six return fields into one sentence is denser than it needs to be.

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 usefully enumerates the returned descriptor fields, which is the main thing an agent needs. It leaves open whether the list is bounded, ordered, or paginated, a minor gap for a zero-argument listing tool.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 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 concrete resource (arena-eligible targets) and even defines the eligibility predicate — services with a paid endpoint that carries a price — plus the descriptor fields returned. It never names the obvious siblings (arena_quote, arena_run), so differentiation is only implied by the 'carries no prices' note rather than stated.

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: this is the discovery/listing step, and the 'carries no prices' line hints that a pricing call is a separate tool. But there is no explicit when-to-use, when-not-to-use, or named alternative, so the agent must infer the workflow.

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