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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description still adds two items annotations cannot express: authentication is required, and the empty-parameter example shows the tool can be called with no arguments. It doesn't mention pagination behaviour for the `limit` field, which keeps it short of a 5.

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?

Short and front-loaded: the WHEN clause and sibling differentiation arrive before the auth note and example. The leading 'Intro inbox.' sentence merely restates the title and the example is arguably redundant with the schema's empty `required` array, costing it a point.

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?

An output schema covers return values, annotations cover the safety profile, and the schema documents both parameters. The description fills the remaining gaps — when to use, which siblings to avoid, and the auth requirement — so an agent has everything needed to invoke it correctly.

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 description coverage is 100% for both optional parameters (key, limit), so the baseline of 3 applies. The `{}` example reinforces that all parameters are optional but adds no semantics about limit ranges or auth precedence between `key` and the Authorization header.

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 and resource — 'list your incoming/outgoing intro requests' — and immediately distinguishes itself from arena_dm_inbox (DMs) and arena_intro_respond (acting on a single request). An agent can pick it over both siblings without opening a 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?

The 'WHEN:' clause names the trigger condition, and the description names both relevant alternatives plus what each does instead. Exclusions and alternatives are explicit, not inferred.

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