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

Annotations already declare a safe read-only, non-destructive operation, so the description only needs to add context. It does: a stated cost of 1 credit and a plan-based gate on the precision and conversions options, which are real behavioral constraints an agent must know before calling.

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 compact and front-loaded, moving from scope to call pattern to optional flags to cost. Minor waste in restating the name twice ('Unit Converter: Unit Converter converts'), but nothing else 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?

For a five-parameter, fully documented tool with an output schema, the description covers scope, required inputs, plan-gated options and cost. An agent has enough to invoke it correctly; only the sibling-selection question is unaddressed.

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%, so the baseline is 3, and the description largely restates what the schema documents for value/from/to. It adds one piece of genuine extra meaning — that precision and conversions only take effect on paid plans — but otherwise does not deepen parameter semantics.

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 ('converts values between 185 units across 23 measures') and enumerates the measure categories (length, mass, volume, speed, pressure, data size, energy, electrical). Those categories implicitly separate it from sibling converters like CurrencyConverter, ColorConverter and NumberBaseConverter, though no sibling is named outright.

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 explains the calling pattern ('Pass a numeric value with source and target unit codes') and flags that precision/conversions are paid-plan features, which is conditional usage guidance. However, it never states when to prefer this tool over the many sibling converters, leaving that inference to the agent.

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