Is CRC16 a cryptographic hash?

No. Like its 32-bit relative CRC32, CRC16 was designed purely to catch accidental bit errors, disk glitches, serial-line noise, transmission corruption, and it's straightforward to construct two different inputs that produce the same CRC16 value on purpose. It offers no resistance to a deliberate adversary, so it should only ever be used for error detection, never for integrity verification against tampering.

Which CRC16 variant does this tool use?

CRC-16/ARC (also called CRC-16/IBM or CRC-16 in many legacy tools): polynomial 0x8005, reflected input and output, initial value 0, no final XOR. It's one of the most common 16-bit CRC parameter sets, but not the only one; CRC-16/CCITT-FALSE, CRC-16/MODBUS, and others use different polynomials or initial values and will not produce matching results for the same input.

Why is the output only 4 characters?

CRC16 produces a 16-bit result, and 16 bits written as hexadecimal is exactly 4 characters (4 bits per hex digit). That short output is intentional: CRC16 was built to be cheap to compute on constrained hardware, not to resist brute-force guessing, so a small output size was never a security concern the way it would be for a cryptographic hash.

Does this tool send my text to a server?

No. CRC16 is computed entirely client-side in JavaScript, so nothing you type here is transmitted anywhere.

CRC16 Calculator - Compute CRC16 Online

Overview

Introduction

CRC16 isn't a hash function in the cryptographic sense, it's a lightweight error-detecting checksum, designed to catch the kind of accidental corruption that happens on disks, serial lines, and older file-transfer protocols.

This tool computes the standard CRC-16/ARC checksum of any text you provide, entirely in your browser, matching one of the most widely used 16-bit CRC parameter sets.

What Is CRC16 Calculator?

CRC16 (16-bit Cyclic Redundancy Check) is an error-detecting code based on polynomial division over GF(2), producing a 16-bit checksum shown here as 4 hexadecimal characters.

This tool implements the CRC-16/ARC variant specifically (polynomial 0x8005, reflected, initial value 0, no final XOR), one of several parameter sets that all share the name "CRC16" but produce different results; ARC is the most commonly seen default across general-purpose CRC tools.

How CRC16 Calculator Works

Each byte of your UTF-8 encoded text updates a running 16-bit register by XORing it against a precomputed lookup table (built from the reflected 0xA001 form of the 0x8005 polynomial), one table lookup per byte.

The register starts at 0x0000, and no final transformation is applied before hex-encoding the result into the 4-character output, matching the CRC-16/ARC convention.

When To Use CRC16 Calculator

Use CRC16 to detect accidental corruption in contexts with limited computational resources: legacy serial protocols, older disk formats, and lightweight embedded file-transfer checks commonly use a 16-bit CRC.

Never use it where someone might deliberately tamper with data and want their tampering to go unnoticed, it offers no resistance to a motivated attacker constructing a colliding value.

Often used alongside CRC32 Calculator and Adler-32 Calculator.

Features

Advantages

Extremely fast and cheap to compute, even more lightweight than CRC32, which is part of why it shows up in older and more constrained hardware protocols.
Good at catching accidental, random-noise-style corruption on small to medium-sized data, its original design goal.
Widely implemented across serial, disk, and legacy file-transfer tooling using the same CRC-16/ARC parameters.

Limitations

Not cryptographically secure in any sense; deliberately constructing a colliding value is straightforward.
Shorter 16-bit output than CRC32 means accidental collisions become statistically likely on much smaller datasets (the birthday bound kicks in around just 256 items).
Several incompatible CRC16 variants exist (ARC, CCITT-FALSE, MODBUS, XMODEM, and more); this tool implements only CRC-16/ARC.

Examples

The standard CRC-16/ARC check value

Input

123456789

Output

bb3d

This is the official published check value for CRC-16/ARC, the standard reference test for confirming any implementation of this exact variant.

Hashing a short greeting

Input

Hello, world!

Output

9a4a

13 bytes of UTF-8 text produce the standard 4-character CRC-16/ARC checksum.

Best Practices & Notes

Best Practices

Use CRC16 for accidental-corruption detection only, never as a stand-in for a cryptographic integrity check.
If tampering resistance matters at all, pair CRC16 (for fast accidental-error detection) with a cryptographic hash like SHA-256 for actual integrity verification.
Remember there are several incompatible CRC16 variants; confirm which one another tool or protocol expects before comparing values, since a mismatch usually means a different polynomial or initial value, not a bug.

Developer Notes

This tool implements the standard table-based CRC-16/ARC algorithm (polynomial 0x8005, reflected as 0xA001, initial value 0x0000, no final XOR), the same convention used by protocols like Modbus's ASCII mode and many legacy serial/disk checks. It's verified against the standard published check value for "123456789" (0xBB3D).

CRC16 Calculator Use Cases

Verifying data integrity in legacy serial, disk, or embedded file-transfer protocols that specify CRC-16/ARC
Building a lightweight, fast integrity check for constrained or non-adversarial internal data pipelines
Reproducing a known CRC16 value while debugging protocol or firmware code
Cross-checking a checksum value against other CRC-16/ARC tooling

Common Mistakes

Using CRC16 to verify data hasn't been maliciously tampered with; it offers no resistance to a deliberate attacker.
Assuming all "CRC16" implementations agree without checking; several variants exist with different polynomials, initial values, or bit conventions, and this is the single most common source of mismatched CRC16 values.
Treating a CRC16 match as strong proof of integrity for anything but small datasets, where its short 16-bit output makes accidental collisions comparatively likely.

Tips

If your value doesn't match another tool's CRC16 output, check which named variant it uses (CCITT-FALSE and MODBUS are common alternatives to ARC) before assuming either implementation is wrong.
For anything where tampering resistance matters, pair this with the SHA-256 tool rather than relying on CRC16 alone.

CRC16 Calculator