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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld. The description adds genuinely useful context beyond them: exact rationals (precision behavior), a per-call price with payment rail, and a parallel HTTPS endpoint. It does not explain how direction (s vs ms) is determined, which is a real behavioral gap.

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?

Front-loads the core purpose in the first sentence and keeps supporting facts short. The pricing and endpoint sentences are extra but directly relevant to invocation, so little is wasted.

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 converter with no output schema, the main missing piece is the input format and unit-detection rule. The pricing and endpoint notes round it out, but the ambiguity of the sole parameter leaves a meaningful hole.

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% and there is a single required 'value' string of maxLength 80. The description never shows the expected input syntax (e.g., '1.5s', '500ms', or a bare number) or how units are interpreted, so the agent must guess the only parameter's format.

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: convert a CSS time between seconds and milliseconds. The domain qualifier 'CSS time' distinguishes it from siblings like css_length, css_angle, and css_resolution, and the note that minutes are not a CSS time unit tightens the scope.

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 by the purpose. It never says when to choose this over unit_convert, duration_parse, or timestamp_convert, nor when not to use it.

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