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

The readOnlyHint annotation already signals a safe read operation, and the description adds valuable output behavior: what combinations are computed, which contrast grades (AA/AAA normal/large) are included, and that a summary is returned. It does not cover edge cases like invalid hex values, but the schema provides type/format coverage, so the marginal disclosure is solid.

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 concise sentences: the first states the action and output, the second captures the key usage decision. Every word contributes without redundancy, making it easy to parse for an agent.

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?

Given the tool has one parameter, a 100% schema-covered parameter description, an output schema, and read-only annotations, the description provides all necessary context: what it computes, the output structure, and when to choose it. It is fully adequate for an agent to invoke 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?

The schema description covers the parameter fully (array of hex values with an example), so the baseline is 3 even without extra detail in the description. The description only says 'palette array,' adding no new semantics beyond the schema, so no increase.

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?

The description opens with a specific action ('Accept a palette array and return every foreground/background combination') and clearly distinguishes itself from the sibling tool accessibility_check by stating it computes a full matrix rather than single checks. This is a concrete verb+resource pairing with clear scope.

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?

It explicitly tells the agent when to use this tool: 'Use this instead of calling accessibility_check multiple times for a palette.' This names the alternative and gives a reason (avoiding multiple calls), which is strong guidance for tool selection.

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