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 clear. The description adds the list of supported units but says nothing about precision, rounding, or return format (output schema exists). It is adequate but not rich.

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?

The description is a single, front-loaded sentence with zero waste. It could arguably include a brief usage note without becoming verbose, but as written it is efficient and appropriately sized for a simple converter.

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?

Given the simple 3-parameter schema, existing output schema, and present annotations, the description covers the essentials. The main missing piece is routing guidance relative to sibling conversion tools, but it is otherwise complete for calling the tool correctly.

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%, establishing a baseline of 3, but the schema lacks enums and its descriptions are terse ('Source length unit.'). The description's enumeration of accepted units (mm, cm, m, km, inch, feet, yard, mile) meaningfully clarifies what strings to use for from_unit and to_unit, adding value beyond the schema.

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 clear verb ('Convert') and resource ('length'), and enumerates the supported units, making the tool's scope obvious. It does not explicitly distinguish itself from sibling conversion tools like calculator_convert or calculator_volume_convert, which keeps it from a 5.

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 description gives no guidance on when to use this tool versus alternatives such as calculator_convert (which may handle other unit types) or other calculators. There are no exclusions or context cues beyond the implied 'length' domain.

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