Overview
isEven is a humorous free API that tells you whether a number is even or odd. It is intentionally over-engineered as a joke, turning a one-line math problem into an API call. It is a fantastic first API to practice HTTP requests because it requires no authentication and has the simplest possible input and output.
Beginner Tip
Just append any integer to the endpoint URL and you will get a JSON response immediately with no setup, no API key, and no authentication needed. This is the perfect API to test your first fetch() or curl command.
Measurement Record
What actually happened when we called this API from our own infrastructure. Every value below was recorded by the request, not copied from the provider's documentation.
- Request
- GET https://api.isevenapi.xyz/api/iseven/42
- Result
- HTTP 200 · application/json · 101 bytes
- Response time
- 147 ms (median of 3) · fastest 136 ms
- Transport
- TLSv1.3 · TLS_AES_256_GCM_SHA384 · certificate issued by Let's Encrypt
- Browser CORS
- Allowed — Access-Control-Allow-Origin: *
- Served by
- nginx/1.18.0
- Recorded
- 2026-08-10
Fields Returned
Top-level fields present in the response we captured, with the type and value we actually received.
| Field | Type | Value received |
|---|---|---|
| ad | string | For sale: human skull. Used once only. $200 O… |
| iseven | boolean | true |
Captured Response
Captured from a real request to https://api.isevenapi.xyz/api/iseven/42 on 2026-08-10. Long arrays and nested objects are truncated to keep the shape readable.
{
"ad": "For sale: human skull. Used once only. $200 OBO Dr. Scott Tyler, 454-555-6533",
"iseven": true
} Field Reference
iseven True if the number is even, false if it is odd. ad A humorous advertisement shown on the free tier; safe to ignore. Implementation Example
Calls a real endpoint of this API. Replace any placeholder credentials with your own key.
const url = "https://api.isevenapi.xyz/api/iseven/42";
const response = await fetch(url);
if (!response.ok) throw new Error(`Request failed: ${response.status}`);
const data = await response.json();
console.log(data); What Can You Build?
Note: These code examples are AI-generated and unverified. Always refer to the official API documentation for accurate usage.
How This API Fails
We deliberately sent this API a broken request and recorded exactly what came back on 2026-08-10. Knowing the shape of an error before you hit it makes error handling much easier to write.
Returned an HTML error page rather than JSON — worth knowing if your client assumes every response can be parsed as JSON.
Common Errors & Troubleshooting
Generated guidance based on this API's documentation, not observed by us. Treat it as a starting point and check against the provider's own error reference.
Measured Score Breakdown
Live HTTP request to the API endpoint
Fully tested on Aug 10, 2026
Technical Specifications
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