Check primality and nearest primes.. Prime Checker is a free online tool from the ToolsRift Math Calculators collection. It runs entirely in your browser — nothing to install, no signup, and your data never leaves your device.
Enter any whole number and the tool reports whether it is prime and shows the nearest prime numbers on either side.
A prime number greater than 1 has exactly two divisors: 1 and itself, so it cannot be evenly divided by any other number.
The checker tests divisibility by integers up to the square root of the number — enough to confirm primality efficiently.
No — 1 has only a single divisor, so by definition it is neither prime nor composite.