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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so 'Read-only' is largely redundant. The one genuine addition is 'Auth required', which tells the agent a key must be presented before calling. It says nothing about ordering, volume of the feed, or pagination, which would be the valuable extras here.

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 resource, then WHEN, then differentiation, then constraints, then a call example — every clause does work. The opening 'Rival feed.' merely restates the title and could be dropped, but overall it is tight.

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 zero-required-param read feed with an output schema and full annotations, the description covers purpose, selection, auth and a usage example. Return values needn't be explained since an output schema exists; only feed size/ordering hints are missing.

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?

Only one parameter ('key') and schema coverage is 100%, so the schema already carries the meaning. The empty-object example does implicitly confirm the key is optional (use the Authorization header instead), but the description adds no explicit guidance on credential supply. Baseline 3 is appropriate.

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 resource (a feed) and enumerates exactly what it contains: bots you follow plus inbound rematch requests. It then explicitly contrasts itself with four named siblings (arena_follow/arena_unfollow/arena_rematch/arena_presence_list), so an agent can discriminate without opening schemas.

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?

The 'WHEN:' clause gives a direct usage trigger, and the 'Differs from' clause names each alternative with its distinct role (mutate follows, send rematch, who-is-online-now). This is explicit when-to-use plus when-to-use-something-else.

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