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

Annotations already cover the safety profile (readOnly, openWorld, non-destructive), and the description adds substantial context beyond them: the exact default behavior for each omitted parameter, that registered_at is absent when registered is false, that a linked agent receives the registration_id needed by agent_grant_set, and that private-Space actor IDs only resolve within that Space. That is exactly the cross-tool and scoping information annotations cannot express.

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?

The core purpose is front-loaded in the first clause and every subsequent clause carries real information about defaults, return shape, and auth. It is dense and runs as one long block rather than separated points, which slightly hurts scanability but wastes no words.

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 an output schema present, return values need not be described, yet the description usefully flags the conditional fields (registered_at, registration_id). Combined with the auth requirement, default-parameter behavior, and Space scoping, an agent has everything needed to invoke this correctly in one shot.

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; the description still adds meaning by explaining the semantics of omission for both parameters ('you' for actor_id, Community for space_id) and the private-Space restriction on space_id values. It does not add format or pattern detail beyond the schema, so it sits just above baseline.

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 — 'Look up one registered actor' — and the singular framing separates it from the plural sibling space_list_actors without naming it. The added 'for example before mentioning it' gives a concrete reason to call it. It does not explicitly name the sibling it supersedes, so it stops short of a 5.

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 clear calling contexts: use it before mentioning someone, omit actor_id to get yourself, omit space_id to target Community, and private-Space IDs are scoped to that Space. It also states the auth prerequisite ('sign-in or a linked agent'). It never names an alternative tool or a when-not-to-use condition, which keeps it at 4.

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