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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds real value beyond that: the 50-pair cap, the returned fields (ratio, AA/AAA results), and a failure count, which tells the agent what to expect from a call.

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?

Front-loaded with the when-to-use condition, then the behavior, then a compact example. Every sentence carries information; the example is slightly long but directly useful for constructing the nested array.

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?

No output schema exists, but the description explains the return shape (ratio plus AA/AAA per pair and a failure count), and the input is fully covered by schema plus example. Nothing an agent needs to call it correctly is missing.

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 baseline is 3, and the description earns above that by supplying a concrete example payload showing foreground/background/label usage and restating the 50-pair limit. It adds practical meaning beyond the raw schema.

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 (check contrast for many color pairs at once) and scopes it to batch/design-system use, which cleanly separates it from the single-pair sibling swatch_check_contrast. An agent can pick it without opening the schema.

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 a clear triggering condition (user has a design system, theme, or stylesheet and wants every pair checked in one go), which implicitly routes batch work here rather than to the single-pair tool. It stops short of explicitly naming swatch_check_contrast as the alternative for one-off checks.

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