apca-contrast

Name: apca-contrast
Availability: InStock
Author: thrillmade

Calculate APCA lightness contrast for text-on-surface accessibility.

1|Updated May 15, 2026

Search Tags:#accessibility #WCAG #contrast #color #APCA

Ready to run

npx skills add https://github.com/thrillmade/agent-skills --skill apca-contrast

💬 Prompt for ChatGPT / Claude Chat▼

Please help me install this Agent Skill.
Skill: apca-contrast
Source: https://github.com/thrillmade/agent-skills/tree/main/skills/apca-contrast
Command: npx skills add https://github.com/thrillmade/agent-skills --skill apca-contrast

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill requires apcach, and includes scripts (resource) and references (resource) components.

What problem does it solve?

This Skill helps in selecting appropriate text-on-surface contrast for accessibility, auditing contrast budgets, and generating colors against specific contrast targets, ensuring compliance with APCA and WCAG 2.2 AA standards.

Core Features & Use Cases

APCA Contrast Calculation: Calculates Lc (lightness contrast) on a 0–105+ scale for text-on-surface contrast.
Palette Generation: Generates palettes targeting specific Lc bands for consistent readability.
Code Review: Flags contrast picks using WCAG 2.x as the primary model instead of APCA.
Use Case: When designing a user interface, use this Skill to check the contrast of text elements against their background to ensure accessibility.

Quick Start

Generate a color with Lc 75 contrast against a white background using the apca-contrast skill.

Frequently Asked Questions about apca-contrast

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I calculate text-on-surface contrast using APCA?▼

APCA contrast is calculated by computing lightness contrast (Lc) on a 0–105+ scale for text-on-surface pairs, providing an accurate perceptual contrast measurement for UI design and accessibility audits.

What is the difference between APCA Lc values and WCAG contrast ratios?▼

APCA Lc values differ from WCAG contrast ratios by modeling perceptual lightness contrast specifically for text-on-surface, whereas WCAG uses a simpler ratio. This Skill flags WCAG-only picks to encourage APCA compliance for better readability.

How do I generate a color palette that meets specific APCA contrast targets?▼

You can generate a color palette targeting specific Lc bands by providing a background color and desired contrast level. This ensures consistent readability across UI elements while maintaining APCA and WCAG 2.2 AA compliance.

Do I need the apcach library to calculate APCA contrast?▼

Yes, the apcach library is required as a dependency to perform inverse composition and calculate APCA lightness contrast, enabling accurate Lc value generation and palette creation for accessibility auditing.

When should I use APCA over standard WCAG contrast models for accessibility?▼

Use APCA over standard WCAG contrast models when designing user interfaces, as it provides a more perceptually accurate lightness contrast calculation for text-on-surface, ensuring optimal readability and WCAG 2.2 AA compliance.