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

Annotations only declare readOnlyHint=true and openWorldHint=false, and the description adds substantial behavior beyond them: it returns WCAG contrast ratios, Coolours colour names, and CSS custom properties, and it tells the agent to reuse the CSS verbatim and to hand the URL to the user. It does not cover things like rate limits or whether a palette is persisted, but for a read-only link generator the disclosure is rich.

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?

The purpose is front-loaded in the first sentence, and the following sentences each carry actionable guidance (when to use it, how to read the ratios, how to use the CSS and the URL). It is on the long side with a chained "Also returns..." pattern, but almost 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?

With an output schema present, the description need not enumerate return fields, yet it still explains the interpretation of the key values (contrast thresholds of 4.5 and 3) and what to do with the results. An agent has everything needed to call the tool and present the output correctly.

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%, so both parameters (name, colours) are already documented in the schema with format and length details. The description adds no further meaning about parameter syntax or constraints, matching the baseline 3 when the schema does the heavy lifting.

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: "Turn a colour palette you have chosen into a link that opens it in Coolours". An agent immediately knows what it produces and where it goes. However, it never names or distinguishes itself from its siblings export_palette and parse_palette_link, so the reader cannot tell from the description alone which of the three to pick.

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?

Gives clear context: "Use this whenever you propose a colour scheme, so the user can see it rather than read hex codes", and prescribes how to act on the output (check contrast before recommending a text/background pairing). It stops short of naming alternatives or exclusion conditions versus the sibling tools, so it is a strong context statement rather than full when/when-not guidance.

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