Build a luminance scale

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered; the description adds real context by describing the return payload and by equating custom targets with 'dragging the site sliders'. It stops short of stating precedence when both a preset and explicit lums are supplied, which is the one behavioral ambiguity that matters for correct invocation.

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 compact sentences with the return payload front-loaded and the usage modes trailing. The '(step 1 on the site)' aside is the only filler, and it ties the tool to an external reference the agent cannot see.

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?

There is no output schema, so the description must explain the return value, and it does by naming the three returned fields. For a read-only, zero-required-parameter tool this is nearly sufficient, with only the preset-vs-lums precedence left unstated.

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%, including enum values and ranges, so the schema carries the parameter detail and the baseline of 3 applies. The description only restates the three modes at a high level, adding no syntax, units or interaction rules beyond what the schema already documents.

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 ('Return the grayscale luminance scale') and enumerates the payload ('luminance targets, shade labels and the gray for each shade'), so the agent knows exactly what comes back. It does not name or contrast any sibling such as generate_palette or adjust_shade, so the distinction is left implicit.

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?

'Use a preset, change the shade count, or pass custom targets' outlines the three invocation modes, which is useful implied guidance on how to call it. However, it never says when to choose this tool over generate_palette or adjust_shade, nor whether the modes can be combined.

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