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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower; the description still adds real context: exact rational arithmetic, a per-call price of $0.001 USDC via x402 on Solana, and an equivalent HTTPS GET endpoint. That is meaningful operational disclosure beyond the structured fields, though it says nothing about failure or payment-failure behavior.

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?

Five short sentences, front-loaded with the action and the unit set, followed by conversion facts, precision guarantee, and payment/transport details. Nothing is redundant or padded.

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 conversion with no output schema, the key missing piece is what comes back: a single converted value in a requested unit, or all three units at once. Without that, the agent cannot tell how the target unit is expressed, which is a material gap for an otherwise well-specified tool.

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?

Only one parameter and schema coverage is 0%, so the description must compensate. It clarifies the unit aliases ('x' means dppx) and the exact conversion ratios, which helps an agent guess the value syntax, but it never explicitly states that value is a unit-suffixed string such as '96dpi' or defines a target unit.

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 resolution') and names the exact unit family (dppx, dpi, dpcm), which separates it from css_angle, css_length, css_time and the generic unit_convert. An agent can identify the right tool without opening the schema.

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 implies usage through the unit family it covers, but never says when to prefer this over unit_convert or the other CSS unit tools, nor does it state any preconditions. Usage is inferable but not stated.

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