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. The description adds genuinely useful context beyond that: the projection model (0.1 mm widening per decade), the default horizon of 20 years, and the important caveat that this is illustrative arithmetic rather than a measurement.

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?

A single front-loaded paragraph: the usage trigger comes first, then what is computed, then the caveat. Every sentence carries information, though it is on the denser end for what is essentially a three-parameter calculation.

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 annotations covering safety, a full schema, and an output schema, the description only needed to convey purpose, trigger and the model's caveat — all of which it does. Nothing an agent needs to invoke this correctly is missing.

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 100%, so the baseline is 3; the description goes beyond the schema by explaining the widening rule that gives `years` and the two width parameters their meaning, and by confirming the default of 20 years. It does not add unit or boundary detail beyond what the schema already states.

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 names a specific computation (projecting line width and gap over time under a stated 0.1 mm/decade rule) and the concrete question it answers. It is unmistakably distinct from siblings like get_tattoo_size_chart or compare_tattoo_placements, which handle different concerns.

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 gives a clear trigger: use when the user supplies a line width and a gap in millimetres and asks whether the gap will stay open with age. No explicit exclusions or named alternative tools are given, but the sibling set is far enough away that routing is unambiguous.

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