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

The description adds behavioral context beyond the annotations: the image is cropped round, the operation takes a few seconds, and the status transitions from cropping to ready. It also adds a consent requirement. This goes beyond the basic readOnly/destructive/idempotent flags.

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 short sentences, each earning its place: action, behavior/status, and usage policy. Front-loaded with the core purpose, no filler or redundancy.

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 add operation, the description covers the main behavioral outcome and the consent constraint, and an output schema exists. A minor gap is that all parameters are optional, so the description does not clarify whether at least one image source is required, but this is relatively minor given the overall clarity.

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 input schema already provides descriptions for all 5 parameters (100% coverage), so the baseline is 3. The description reinforces the 'face' concept and crop behavior but does not add parameter-specific details beyond what the schema states, nor does it clarify the relationship between image_url and image_base64.

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 states a specific action and resource: 'Add a face to the people library.' This clearly distinguishes it from sibling tools like list_people, delete_person, and upload_media, leaving no ambiguity about what the tool does.

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 provides clear context for when to use the tool (adding a person to the people library) and an explicit policy condition ('Only upload people who agreed'). It does not explicitly compare alternatives or state when not to use it, but the context is strong enough to guide selection.

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