Color Brightness Calculator API

GET

Know if any color is light, medium, or dark.

Color Brightness Calculator checks hex color brightness to classify values as light, dark, or medium, returning RGB components. Paid plans add WCAG contrast ratios, luminance scores, and recommended text colors.

Try it — live request, no key required

Request

GETapi.apiverve.com/v1/colorbrightness?hex=FF5733

Query parameters

hexstring

Verification

Format

No key required to try it. Get a key to use it in your app.

Example

{
  "status": "ok",
  "error": null,
  "data": {
    "hex": "#FF5733",
    "rgb": {
      "r": 255,
      "g": 87,
      "b": 51
    },
    "luminance": 0.2832,
    "perceived_brightness": 131,
    "yiq": 133.13,
    "is_light": false,
    "is_dark": true,
    "brightness_category": "dark",
    "recommended_text_color": "#FFFFFF",
    "contrast_ratio_with_white": 3.15,
    "contrast_ratio_with_black": 6.66,
    "wcag_aa_compliant_with_white": false,
    "wcag_aa_compliant_with_black": true,
    "wcag_aaa_compliant_with_white": false,
    "wcag_aaa_compliant_with_black": false
  }
}

About the Color Brightness Calculator API

Color Brightness Calculator works by applying WCAG 2.0 relative luminance formulas to RGB color values, calculating contrast ratios with black and white, and determining optimal text colors for accessibility.

What people use it for

Web Accessibility: Ensure WCAG compliance by calculating contrast ratios for text and background colors
UI Design: Determine appropriate text colors for backgrounds based on brightness calculations
Theme Development: Automatically select light or dark text based on background color brightness
Color Analysis: Analyze color brightness and categorize colors for design systems and palettes

Ways to call it

One endpoint, many ways in — REST with JSON, XML, YAML and CSV, plus GraphQL and an MCP interface for AI agents.

JSON: Default REST response
XML: Markup format
YAML: Human-readable
CSV: Tabular export
GraphQL: Query language
MCP: For AI agents

View all integrations →

Other ways to use Color Brightness Calculator

Same data, same APIVerve account, same credit balance — one key works on all of them.

Give it to an AI agentConnect over MCP and your agent calls it as a native tool — Claude, Cursor, ChatGPT.on VerveKit Google Sheets or ExcelA =VERVE() formula fills a column — no script, no export, recalculates in place.on VerveSheets Ground an agent on itA cited, machine-checkable fact your model can't produce on its own.on VerveContext

Questions.

Common questions about the Color Brightness Calculator API.

Read the docs →

How are the brightness and contrast ratios calculated?

Calculations follow standard WCAG 2.0 relative luminance formulas applied to RGB values. On paid plans, the API evaluates contrast ratios against black and white to check WCAG AA and AAA compliance thresholds.

Do I get WCAG compliance flags and recommended text colors on the Free plan?

No, WCAG compliance indicators and recommended text colors require a paid plan. The Free plan returns basic RGB components and light or dark classifications. Upgrading to Starter or above unlocks relative luminance, perceived brightness, YIQ scores, contrast ratios, and AA or AAA compliance checks.

Which plan fits 50,000 color checks a month?

The Starter plan covers 50,000 checks comfortably. Each call uses 2 credits, meaning 50,000 checks consume 100,000 of the 200,000 monthly credits available on Starter, working out to about $0.30 per 1,000 calls. The Free plan provides 100 calls per month for evaluation.

Does the API accept hex codes without a hash symbol?

Yes, hex color strings can be provided with or without the leading # character. Both formats are parsed directly into their RGB components.

Does the check evaluate both WCAG AA and AAA standards?

Yes, on paid plans, the API evaluates both WCAG AA and WCAG AAA compliance levels. It provides separate boolean results for black and white pairings across both tiers along with the raw contrast ratios.

Request parameters — GET /v1/colorbrightness

Sent in the query string. Premium parameters are accepted on every plan but only take effect on plans that include them. Anything not listed here is dropped rather than passed through.

Required

Parameter	Type	Example	Description
`hex`Required	string	`FF5733`	Hex color value (with or without # prefix) hexColor

Example request

1
2

curl "https://api.apiverve.com/v1/colorbrightness?hex=FF5733" \
  -H "x-api-key: YOUR_API_KEY"

Authentication

Send your key in the x-api-key header. That is the only auth step — no token exchange, and no per-endpoint scope to configure.

Header	When	Value
`x-api-key`Required	Every request	Your API key. Header names are case-insensitive, so `X-API-Key` is the same header.
`Authorization`Alternate	Instead of the above	`Bearer <key>` — for clients that only expose bearer auth. Resolves to the same account and the same billing.

401 is the only auth verdict

A 401 means the key is missing, invalid or expired. A 403 means the key is valid but not permitted here — blocked by a key restriction or an IP allow-list. Running out of credits is a 429.

Response — GET /v1/colorbrightness

Every APIVerve endpoint returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape.

Sample response

{
  "status": "ok",
  "error": null,
  "data": {
    "hex": "#FF5733",
    "rgb": {
      "r": 255,
      "g": 87,
      "b": 51
    },
    "luminance": 0.2832,
    "perceived_brightness": 131,
    "yiq": 133.13,
    "is_light": false,
    "is_dark": true,
    "brightness_category": "dark",
    "recommended_text_color": "#FFFFFF",
    "contrast_ratio_with_white": 3.15,
    "contrast_ratio_with_black": 6.66,
    "wcag_aa_compliant_with_white": false,
    "wcag_aa_compliant_with_black": true,
    "wcag_aaa_compliant_with_white": false,
    "wcag_aaa_compliant_with_black": false
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Field	Type	Example	Description
`hex`	string	`"#FF5733"`	Hexadecimal color value provided in the request
`rgb`	object	`{...}`	RGB color components: red, green, blue values
`r`	number	`255`	Red component value between 0 and 255
`g`	number	`87`	Green component value between 0 and 255
`b`	number	`51`	Blue component value between 0 and 255
`luminance`Premium	number	`0.2832`	Relative luminance calculated using WCAG 2.0 formula
`perceived_brightness`Premium	number	`131`	Perceived brightness score from 0 to 255
`yiq`Premium	number	`133.13`	YIQ color space brightness value for brightness analysis
`is_light`	boolean	`false`	Boolean indicating if color is considered light
`is_dark`	boolean	`true`	Boolean indicating if color is considered dark
`brightness_category`	string	`"dark"`	Brightness classification: light, medium, or dark category
`recommended_text_color`Premium	string	`"#FFFFFF"`	Recommended text color for optimal contrast and readability
`contrast_ratio_with_white`Premium	number	`3.15`	WCAG contrast ratio calculation between color and white
`contrast_ratio_with_black`Premium	number	`6.66`	WCAG contrast ratio calculation between color and black
`wcag_aa_compliant_with_white`Premium	boolean	`false`	Whether color meets WCAG AA contrast requirements with white
`wcag_aa_compliant_with_black`Premium	boolean	`true`	Whether color meets WCAG AA contrast requirements with black
`wcag_aaa_compliant_with_white`Premium	boolean	`false`	Whether color meets WCAG AAA contrast requirements with white
`wcag_aaa_compliant_with_black`Premium	boolean	`false`	Whether color meets WCAG AAA contrast requirements with black

Response headers

Every response carries your balance, so your own code always knows where it stands without polling anything. All four are exposed to browsers through CORS.

Header	What it carries
`x-api-remaining-credits`	Credits left in the current cycle
`x-api-credits-used`	Credits spent in the current cycle
`x-api-max-credits`	The allowance for the cycle
`x-api-version`	Version of the endpoint that answered

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change.

Status	Meaning	What to do
`400`	Input was rejected	Read `error`; it names the parameter that has to change.
`401`	Key missing or invalid	Check the header name and the key value.
`403`	Key valid, but not permitted here	A key restriction or an IP allow-list — never a bad key.
`429`	Rate limited, or out of credits	Read `error` to tell them apart, then back off or top up.

What a call costs — 2 credits per call

Credits are shared across every APIVerve API — one balance, one key, one bill. Failed requests never count against it, so a rejected input costs nothing.

Plan	Per month	Credits	Color Brightness Calculator calls	Per 1,000 calls
Free	Free	200	100	Free
Starter	$29.99	200,000	100,000	$0.30
Pro	$99.99	1,000,000	500,000	$0.20
Mega	$299.99	4,000,000	2,000,000	$0.15

Calls are what the credits buy at this API's rate — spend them here, on any of the other APIs, or across both. Nothing is reserved per endpoint.

Compare all pricing tiers →

Call it from cURL — GET /v1/colorbrightness

No SDK to install — this is a plain HTTPS call to /v1/colorbrightness with your key in the x-api-key header. Swap in a real key and it runs as-is.

cURL

1
2

curl "https://api.apiverve.com/v1/colorbrightness" \
  -H "x-api-key: YOUR_API_KEY"

Resources

GitHubapiverve/colorbrightness-apiSource, issues and the examples this page is built from.ReferenceColor Brightness Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/colorbrightnessnpm APIVerve.API.ColorBrightnessCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Node.js — GET /v1/colorbrightness

Install the Node.js SDK, then call the Color Brightness Calculator API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — npm

npm install @apiverve/colorbrightness

Node.js

const res = await fetch("https://api.apiverve.com/v1/colorbrightness", {
  headers: { "x-api-key": "YOUR_API_KEY" },
});
const { data } = await res.json();
console.log(data);

Resources

npm@apiverve/colorbrightnessThe published Node.js client, versioned and signed.GitHubapiverve/colorbrightness-apiSource, issues and the examples this page is built from.ReferenceColor Brightness Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

APIVerve.API.ColorBrightnessCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Python — GET /v1/colorbrightness

No SDK to install — this is a plain HTTPS call to /v1/colorbrightness with your key in the x-api-key header. Swap in a real key and it runs as-is.

Python

import requests

res = requests.get(
    "https://api.apiverve.com/v1/colorbrightness",
    headers={"x-api-key": "YOUR_API_KEY"},
)
print(res.json()["data"])

Resources

Also published for

@apiverve/colorbrightnessnpm APIVerve.API.ColorBrightnessCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from C# / .NET — GET /v1/colorbrightness

Install the C# / .NET SDK, then call the Color Brightness Calculator API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — NuGet

dotnet add package APIVerve.API.ColorBrightnessCalculator

C# / .NET

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("x-api-key", "YOUR_API_KEY");

var json = await client.GetStringAsync("https://api.apiverve.com/v1/colorbrightness");
Console.WriteLine(json);

Resources

NuGetAPIVerve.API.ColorBrightnessCalculatorThe published C# / .NET client, versioned and signed.GitHubapiverve/colorbrightness-apiSource, issues and the examples this page is built from.ReferenceColor Brightness Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/colorbrightnessnpm

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Go — GET /v1/colorbrightness

No SDK to install — this is a plain HTTPS call to /v1/colorbrightness with your key in the x-api-key header. Swap in a real key and it runs as-is.

req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/colorbrightness", nil)
req.Header.Set("x-api-key", "YOUR_API_KEY")

res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))

Resources

Also published for

@apiverve/colorbrightnessnpm APIVerve.API.ColorBrightnessCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from PHP — GET /v1/colorbrightness

No SDK to install — this is a plain HTTPS call to /v1/colorbrightness with your key in the x-api-key header. Swap in a real key and it runs as-is.

PHP

$ch = curl_init("https://api.apiverve.com/v1/colorbrightness");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-api-key: YOUR_API_KEY"]);

$response = curl_exec($ch);
echo $response;

Resources

Also published for

@apiverve/colorbrightnessnpm APIVerve.API.ColorBrightnessCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Ruby — GET /v1/colorbrightness

No SDK to install — this is a plain HTTPS call to /v1/colorbrightness with your key in the x-api-key header. Swap in a real key and it runs as-is.

Ruby

require "net/http"

uri = URI("https://api.apiverve.com/v1/colorbrightness")
req = Net::HTTP::Get.new(uri)
req["x-api-key"] = "YOUR_API_KEY"

res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h| h.request(req) }
puts res.body

Resources

Also published for

@apiverve/colorbrightnessnpm APIVerve.API.ColorBrightnessCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

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Color Brightness Calculator API

Try it — live request, no key required

About the Color Brightness Calculator API

What people use it for

Ways to call it

Other ways to use Color Brightness Calculator

Questions.

Request parameters — GET /v1/colorbrightness

Required

Authentication

Response — GET /v1/colorbrightness

Response fields

Response headers

Errors

What a call costs — 2 credits per call

Call it from cURL — GET /v1/colorbrightness

Resources

Also published for

Call it from Node.js — GET /v1/colorbrightness

Resources

Also published for

Call it from Python — GET /v1/colorbrightness

Resources

Also published for

Call it from C# / .NET — GET /v1/colorbrightness

Resources

Also published for

Call it from Go — GET /v1/colorbrightness

Resources

Also published for

Call it from PHP — GET /v1/colorbrightness

Resources

Also published for

Call it from Ruby — GET /v1/colorbrightness

Resources

Also published for

Zero-code embed — one snippet, no backend

Changelog — Color Brightness Calculator API

Reference Data

Related articles

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