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

Annotations already indicate this is a mutation (readOnlyHint=false), so the description adds value by disclosing the Premium requirement and that the user becomes owner. There is no contradiction with annotations, and these extra details go beyond the structured metadata.

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 succinct, front-loaded with the core action and requirement, and structured with clear Args/Returns sections. Every sentence serves a purpose with no fluff.

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?

For a simple creation tool with one parameter, the description covers the essential prerequisites and ownership outcome, but the return value is vaguely described as 'Created group details' with no output schema to fill the gap. This leaves some uncertainty about what the agent can expect, so a 3 is appropriate.

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 0%, so the description must compensate for the 'name' parameter. It provides 'name: Group name', which clarifies the purpose but adds little beyond the schema's title. Given the single simple parameter, this minimal addition is adequate, earning a 3.

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 action 'Create a new family group' and specifies the effect 'user becomes owner', distinguishing it from invitation-based siblings like accept_family_invitation or decline_family_invitation. The verb-resource pair is explicit and unambiguous.

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 provides clear context for when to use the tool—creating a new family group—and notes the Premium requirement, but does not explicitly contrast with alternatives or state when not to use it. This is clear context without exclusions, fitting a 4.

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