Color luminance and contrast

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

Annotations already declare readOnly/idempotent/closed-world, so the description would only need to add output-side context — and it does, listing every returned field since there is no output schema. The note that luminance is 'the site's color value, 0-100' is genuinely non-obvious domain context. It omits what happens with an unparseable color string, which keeps it from a 5.

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?

A single waste-free sentence with the verb and resource front-loaded and the return payload following. It is dense — one long clause chain — but nothing is redundant, and trimming further would cost real information.

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 2-parameter read-only tool with full schema coverage and no output schema, the description supplies the return contract and the site-specific luminance scale, which is exactly what structured fields don't cover. Only error/edge behavior for malformed color input 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 coverage is 100%, so the 3 baseline is already met. The description still adds meaning to 'against' by framing it as one of the WCAG contrast targets alongside the always-computed white and black, which the schema's 'Optional second color for a contrast ratio' leaves ambiguous.

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?

Specific verb ('Parse a color') plus an explicit enumeration of the returned representations (hex, rgb, hsl, oklch, luminance, auto name, WCAG ratios), which makes it distinguishable from luminance_scale and adjust_shade on output shape alone. It never names a sibling or states the boundary explicitly, so it stops short of 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?

Usage is only implied: the mention of contrast against white, black and an optional second color signals this is the tool for 'can I read text on this color' checks. There is no when-to-use/when-not and no reference to the palette/sibling tools an agent might otherwise pick.

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