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

Annotations establish read-only/idempotent/non-destructive behavior; the description adds the computational formula, the sign convention for nasal/temporal, and the no-prism limitation. This is useful behavioral context beyond the annotations. There is no contradiction.

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 dense sentence front-loads the formula and follows with sign convention and exclusions; no filler.

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 calculation tool with no output schema, the description covers scope, formula, units, sign convention, and exclusions, which is the core of what an agent needs. It leaves minor gaps such as return shape and language behavior, but these are not critical to correct invocation.

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 0%, so the description must carry parameter meaning; it does for the main inputs by giving the formula with A, bridge, and monocular PD per eye. It does not explain the optional 'language' parameter, but its enum/default in the schema mitigates this.

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 precise calculation formula with scope ('Symmetric boxing frame only'), sign convention ('Positive nasal'), and exclusion ('No vertical or prescribed prism compensation'), making the tool's function unmistakable and distinguishing it from optical siblings like calculate_prism.

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 clearly defines when the tool applies: symmetric boxing frames only, and explicitly excludes vertical and prescribed prism compensation. It does not name a specific sibling as the alternative, so the when-not guidance is present but the alternative routing is left to the agent.

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