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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered without prose. The description adds real value beyond that: it enumerates the returned dimensions (fade, sun, friction, stretch, curvature, style notes, questions for the artist) and discloses the measurement convention, which the agent needs to interpret results. It does not discuss failure modes when size or placement is omitted.

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 sentences, no filler: trigger first, then output content, then scope exclusions. The long middle sentence is dense but every clause maps to a distinct returned field or sizing rule, so nothing is padding.

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, the description need not document return values, and the read-only annotations cover the action profile; the remaining ambiguity is behavioral rather than descriptive. It stops short of saying what happens when only the required design_type is supplied and style, size_cm or placement are omitted, which is a realistic call pattern for this tool given four of five parameters are optional.

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 100%, including per-parameter usage rules for size_cm and letter_height_mm, so the schema already carries the semantics and the baseline is 3. The description restates the lettering-vs-everything-else sizing rule (capital letter height vs longest side), which reinforces rather than extends the schema, adding little new information.

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 and resource ('assess a tattoo idea's size, placement and style') plus the concrete trigger condition (user asks whether a design will hold up at a given size and placement). It also carves out what it is not (design generation, image analysis, medical advice), which separates it from get_tattoo_size_chart and the checklist siblings. An agent can route to it without opening any schema.

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 opening clause is an explicit when-to-use trigger, and the closing sentence gives three clear when-not conditions (does not generate designs, look at images, or give medical advice). It never names a sibling tool as the better alternative for the overlapping 'size chart' case, so the routing versus get_tattoo_size_chart is left to inference.

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