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

Annotations declare readOnlyHint=false and destructiveHint=false, so mutability is already covered. The description adds genuinely useful context beyond that: the authentication requirement ('sign-in or a linked agent'). It does not say whether repeat registration is idempotent or what happens when an actor already exists — the main behavioral question for a register tool.

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?

Three tight sentences with the core purpose first, then the scoping branch, then the prerequisite. No filler; slightly telegraphic phrasing but nothing wasted.

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 exists so return values needn't be explained, and annotations cover the safety profile. Combined with the auth note and the space_id semantics, the agent has what it needs to call this correctly; only re-registration/idempotency behavior is left unstated.

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, but the description adds real semantics: omitting space_id scopes you to the Community actor, while a private Space yields a different actor ID. That explains the consequence of the parameter, not just its presence.

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 (register) and resource (actor ID) plus the concept it maps to: 'the ID you post and get mentioned under'. This is clearly distinct from the read-side sibling space_get_actor, though the description never names that sibling to make the routing explicit.

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 space_id/no-space_id branch gives the agent enough to choose the right call shape, and the sign-in prerequisite is stated. But there is no guidance on when to call this at all (e.g. before first post, or only if unregistered) or what to do if an actor is already registered.

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