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

Goes well beyond the annotations by disclosing the link's single-use nature, its 48-hour expiry, and the security consequence that whoever opens it gains access to the family log. The annotations only say it is a non-read-only, non-idempotent write, so this added access-granting context is genuinely valuable.

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?

Two sentences, front-loaded with the action and lifetime, followed by the access consequence and the return value. Every clause earns its place; nothing is padded.

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 input parameters and no output schema, the description supplies everything needed: what is produced, how long it lasts, that it is single-use, what access it confers, and the name of the returned field (join_url). No gaps remain for an agent to fill.

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 for a no-parameter tool is 4. It sensibly uses the space for scope and behavior instead of inventing parameter detail.

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 (create) and resource (single-use caregiver invite link) plus the exact outcome (someone joins the family and logs events with their own account). No sibling tool does anything similar, so it is trivially distinguishable from the log_*/get_* siblings.

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?

It clearly frames the scenario that calls for it (adding a partner, grandparent or nanny to the family log) and the mechanism (a link the other person opens). It does not name a when-not condition or an alternative invite/role-management tool, but none exists among the siblings, so the context is effectively complete.

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