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

Annotations already declare readOnly=false, idempotent=true, destructive=false. The description adds genuinely non-structured context: the consent/rights requirement, the fact that identity images propagate the face into every later tagged generation, and that an image-less subject still travels as name+description. It never contradicts the annotations.

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?

Front-loads the core purpose, then layers usage, consent, and image behavior with almost no waste. The quoted example ('no mouth, only a stitched black nose') is illustrative rather than padding, though the prose is denser and more stylized than strictly necessary.

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 no explanation, and the description covers the tool's distinctive behaviors (reuse, image propagation, consent). The enum semantics of 'kind' and the distinctions among cover/sheet/avatar are left entirely to the schema, a minor gap for a 10-parameter tool.

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 70%, so the baseline is 3. The description adds real meaning for the identity images ('the face that travels') and the description field (write what it lacks as well as what it has), but says nothing about name, kind, tags, cover, sheet, avatar, voice, or prompt_fragment, leaving the schema to carry those.

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+resource ('Name an identity so it can be reused') and clarifies the reusable-identity concept clearly. It does not distinguish itself from siblings like update_subject or list_subjects, leaving the agent to infer the create-vs-modify boundary.

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 concrete when-to-use guidance ('Offer one when something the user brought appears in a second generation, never unasked') and a clear constraint ('Only for people the user has the right to depict; a real person needs their consent'). It lacks any explicit routing to update_subject for existing subjects, but the creation context is well covered.

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