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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavioral context: the inputs must be opaque hex, the result is "evidence-bounded," and a canonical web tool URL is returned.

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?

Two sentences with zero filler; the core action and its constraint are front-loaded before the return-value note. Every clause earns its place.

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?

Return values are largely covered by the output schema, and the description usefully flags that a web tool URL comes back. "Evidence-bounded result" is slightly internal jargon, but for a two-parameter, read-only calculator this is close to complete.

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 0% for both parameters, so the description must carry semantic weight. It adds that the two colors are hex and must be opaque, but does not specify accepted syntax (e.g. leading '#', 3- vs 6-digit) beyond the maxLength=7 hint.

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 (Calculate) and resource (WCAG text contrast ratio) with a precise scope (two opaque hex colors). No sibling tool covers color analysis, so the agent can identify it uniquely from the name plus this sentence.

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?

"before shipping a landing page or launch graphic" gives clear timing/context for when to reach for it. It does not name alternatives or exclusions, but none of the sibling tools overlap, so there is little risk of mis-selection.

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