isEven API — Free Number Parity Check API (No Key)

TL;DR

The isEven API is a humorous but fully functional parity check service. Submit any integer and it returns whether it's even or odd, plus a random advertisement (the joke is that it monetizes the world's simplest API). Response includes iseven (boolean), ad (promotional text), and adlink (URL). Works for any integer. No API key required.

Quick start: https://api.isevenapi.xyz/api/iseven/6

No API key needed — free parity checking with a smile!

How to Use This API

1. Check if a Number is Even

Returns JSON with iseven field plus a random ad:

https://api.isevenapi.xyz/api/iseven/6

2. Check an Odd Number

https://api.isevenapi.xyz/api/iseven/7

3. JavaScript — Number Checker

function checkEven(num) {
  fetch(`https://api.isevenapi.xyz/api/iseven/${num}`)
    .then(r => r.json())
    .then(data => {
      console.log(`Is ${num} even? ${data.iseven}`);
      console.log(`Ad: ${data.ad}`);
      if (data.adlink) console.log(`Link: ${data.adlink}`);
    })
    .catch(() => {
      // Fallback to client-side check
      console.log(`Is ${num} even? ${num % 2 === 0}`);
    });
}

checkEven(42);
checkEven(13);

4. Python — Silly Script

import requests

nums = [1, 2, 100, 999, 0, -4, -7]
for n in nums:
    resp = requests.get(
        f'https://api.isevenapi.xyz/api/iseven/{n}'
    ).json()
    status = 'EVEN' if resp['iseven'] else 'ODD'
    print(f"{n:>4} → {status:4} | \"{resp['ad']}\"")

Is 6 even? https://api.isevenapi.xyz/api/iseven/6

Try This URL Now

Frequently Asked Questions

Is this a joke API?: Yes — it started as a novelty/meme API that solves the world's simplest computation while serving ads. However, it is fully functional and reliably returns correct parity results.
What's with the ads?: The ad field contains random promotional text and adlink contains an optional URL. This is the API's monetization joke — even checking if a number is even comes with advertising.
Does it work with negative numbers?: Yes — any integer works with the API. Negative numbers follow the same parity rules as positive numbers. -4 is even, -7 is odd.
What about very large numbers?: The API handles integers within JavaScript's safe integer range (up to 9,007,199,254,740,991). For larger numbers, use client-side parity checking.
Is there a rate limit?: 100% free with no rate limits. The API is designed to be fun and accessible. Go ahead and use it as much as you want.
Should I use this in production?: For anything serious, use number % 2 === 0 client-side — it's faster and doesn't require a network request. This API is for fun, learning, and novelty applications.

API Details

API URL: https://api.isevenapi.xyz/api/iseven/{number}
Documentation: isevenapi.xyz
Category: Entertainment
Authentication: Not Required
Response: {iseven: boolean, ad: string, adlink: string}

What You Can Build

Fun demo app for teaching API concepts to beginners
Number trivia widget with parity checking and ads
Discord bot responding with even/odd results
Dev conference demo showing REST API integration
Meme generator combining parity results with random ads