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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds no behavioral context beyond the operation itself (e.g., no note on how zero or near-zero vectors are handled, though the schema's 'Non-zero vector' partially covers that).

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?

One sentence, front-loaded with the verb, with zero filler. Every word carries meaning and nothing is omitted that belongs at this level of detail.

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 one-parameter math utility with an output schema and full annotation coverage, the description is nearly sufficient: it says exactly what transformation is performed. Minor gaps remain around sibling differentiation and edge-case behavior, which are the only things an agent might still need.

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?

There is a single parameter with 100% schema description coverage, so the schema already documents it fully. The description mentions the vector implicitly but adds no format, dimension, or validation guidance beyond what the schema provides; baseline 3 applies.

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 mathematical operation (normalize to unit length) and states the invariant outcome (same direction), which is unambiguous. It does not, however, distinguish itself from nearby siblings such as calculator_vector, calculator_magnitude, or calculator_normal, which an agent could plausibly confuse it with.

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?

Usage is only implied: an agent can infer 'use when you need a unit vector' but there is no explicit when/when-not guidance and no pointer to alternatives like calculator_magnitude or calculator_vector for related operations. Adequate but leaves the agent to reason about selection among ~140 calculator siblings.

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