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

The description discloses important behavioral aspects: it sends an invitation, that only humans can be invited, and that the human owns billing and Approval Inbox. It also states a limitation for agents. This goes beyond the basic annotations, though it does not describe the full side-effect sequence (e.g., whether a principal is created).

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 description is two sentences long, focused, and without unnecessary detail. It front-loads the core action and then adds relevant constraints, making it easy to parse.

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?

The description is complete for the action's scope: it specifies the required input pattern, a key restriction, and an outcome ownership detail. It does not explain error handling or alternative flows, but given the simplicity, it is sufficiently complete.

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 schema descriptions for human_email and principal_id are simple. The tool description adds crucial semantics by indicating that either one should be provided, and that principal_id is an existing human user id. This clarifies the 'or' relationship not explicit in the schema.

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?

The description clearly states the tool's action: 'Invite a human to start the 1-day trial.' The resource is a trial, and the verb is explicit. It also notes the constraint that agents cannot open a root account, distinguishing this from potential related actions.

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 description explains input requirements ('Provide human_email or an existing principal_id') and a constraint, but it does not explicitly compare with sibling tools or specify when this tool is preferred over alternatives like create_checkout or attach_human. Usage guidance is implied rather than fully explicit.

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