palette_contrast_implValidate contrast between foreground and background colors with WCAG or APCA, returning a ratio or Lc score for text readability and accessibility.
Contrast for one fg/bg pair. method='apca' uses the APCA 0.1.9 perceptual algorithm (WCAG 3 draft direction; Lc>=75 body, >=60 large, >=45 bold).
| Name | Required | Description | Default |
|---|---|---|---|
| bg | Yes | ||
| fg | Yes | ||
| method | No | wcag |
| Name | Required | Description | Default |
|---|---|---|---|
| result | Yes |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden, and it does disclose real substance: the APCA 0.1.9 algorithm, its WCAG 3 draft provenance, and the Lc thresholds (>=75 body, >=60 large, >=45 bold). However, it never explains the default 'wcag' method's behavior or whether the tool is a pure read/computation, leaving a notable gap for an annotation-free tool.
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 tight sentences with no filler, and the core purpose ('Contrast for one fg/bg pair') is front-loaded before the method detail. Slightly jargon-dense but appropriately sized.
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?
An output schema exists, so return values need not be described. But with zero annotations the description should more fully cover behavior, and it omits the default 'wcag' method semantics and any routing to the sibling that handles multiple pairs, leaving the definition only partially complete.
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 0% across 3 parameters, so the description must compensate. It does add genuine meaning for 'method' (the 'apca' option and its thresholds) but says nothing about the required 'fg' and 'bg' parameters – their accepted format (hex, rgb, name) is undocumented in both schema and description.
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 operation and scope: 'Contrast for one fg/bg pair.' The 'one pair' phrasing implicitly separates it from batch siblings like palette_matrix_impl or palette_score_impl, but no sibling is named explicitly, so differentiation is inferential rather than stated.
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?
The description gives no when-to-use or when-not-to-use guidance and never names an alternative tool. The implicit signal that this handles a single pair (vs. a matrix/scoring sibling) is the only usage cue, and an agent must infer it.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.