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

Annotations already establish that this is a safe read-only operation, and the description adds meaningful behavior: pair-wise testing thresholds of 4.5:1 and 3:1, nearest passing color suggestions, color-blindness merging detection, tier limits, and a markdown report. It does not mention error handling, but it goes well beyond the annotations.

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 description is front-loaded with the input and core behavior, and its two sentences carry useful specifics. The free/Pro sentence is somewhat promotional but still conveys a practical capacity limit, so it mostly 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?

For a one-parameter read-only tool with no output schema, the description covers input formats, processing behavior, contrast thresholds, ancillary checks, limits, and return format. That is nearly complete, with only error handling left 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 baseline is 3, but the description adds useful parameter-level meaning by enumerating supported token formats (CSS custom properties, JSON color object, W3C design tokens) and giving a concrete CSS example. That compensates for the terse schema description 'The token file contents'.

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 states a specific verb and resource: taking a design token file and testing foreground/background token pairs for contrast. The phrase 'design token file' helps distinguish it from generic contrast-checking siblings, though it never names an alternative directly.

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 implied by 'Take a design token file' and the accepted input formats, so an agent can infer when it applies. However, it gives no explicit when-to-use or when-not-to-use guidance relative to siblings like check_contrast and css_contrast_pairs.

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