ForHosting KIT · Developer Utilities

WCAG contrast ratio checker

This WCAG contrast ratio checker takes two hex colors—foreground and background—and returns the official contrast ratio used by Web Content Accessibility Guidelines, together with clear AA and AAA pass or fail flags for both normal text and large text.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Designers, developers, and auditors use that ratio to decide whether body copy, buttons, labels, and UI chrome remain readable for people with low vision or color-vision differences. The engine follows the WCAG 2.x relative-luminance formula: each hex channel is linearized from sRGB, luminance is weighted with the standard 0.2126, 0.7152, and 0.0722 coefficients, and the contrast ratio is (L lighter plus 0.05) divided by (L darker plus 0.05). Thresholds are unrounded: normal text needs at least 4.5 for AA and 7 for AAA; large text needs at least 3 for AA and 4.5 for AAA. Results are deterministic with no network calls, sampling, or date-dependent shortcuts. Use it free in the browser for palette reviews and design tokens, or call the API at $0.002 per successful request when you need the same matrix in CI, design systems, or automated accessibility gates.

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

How do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/color/contrast

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/color/contrast \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"foreground":"#111827","background":"#ffffff"}'

const res = await fetch("https://api.kit.forhosting.com/color/contrast", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "foreground": "#111827",
    "background": "#ffffff"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/color/contrast",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "foreground": "#111827",
    "background": "#ffffff"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/color/contrast", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"foreground":"#111827","background":"#ffffff"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"foreground":"#111827","background":"#ffffff"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/color/contrast", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "foreground": "#111827",
  "background": "#ffffff"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "color.contrast",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

max_color_chars 32

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →

Run — free