Which CRC-64 variant does this tool compute?

CRC-64/XZ (also called CRC-64/GO-ECMA), using the reflected polynomial 0xc96c5795d7870f42 with a zero-complemented initial value. It's the checksum built into the .xz compression format's container, and its official published check value for the ASCII string "123456789" is 0x995dc9bbdf1939fa, which this tool's implementation matches exactly.

Why use CRC-64 instead of CRC-32?

CRC-32's 32-bit space starts producing meaningful collision odds once you're checksumming very large numbers of files or very large data volumes (the birthday bound puts a 50% collision chance around 77,000 random 32-bit checksums). CRC-64's 64-bit space pushes that bound astronomically further out, which is exactly why formats built for big archives and streams, like xz, chose a 64-bit checksum over the 32-bit CRCs common in older formats like zip and gzip.

Why is this the only CRC tool in this category computed asynchronously?

It's computed via hash-wasm, a WebAssembly implementation, the same reason this category's Whirlpool tool is also async: rather than hand-rolling a 64-bit CRC table and risking a subtle correctness bug in JavaScript's 32-bit-oriented bitwise operations, this defers to hash-wasm's audited WASM binary, which returns its result as a Promise.

Does this tool send my text to a server?

No. The CRC-64 checksum is computed via a WebAssembly module that runs entirely inside your browser, not on a server, so nothing you type here is transmitted anywhere.

CRC64 Calculator - Compute CRC-64/XZ Checksum Online

Overview

Introduction

CRC-64 is the largest checksum in this category, a 64-bit result built into formats like xz that need much lower collision odds than CRC-32 provides across large archives and streams.

This tool computes the CRC-64/XZ variant of any text you provide, running entirely in your browser via WebAssembly, useful for verifying an xz-style checksum or matching known reveng CRC-catalogue test vectors.

What Is CRC64 Calculator?

CRC-64 is a 64-bit cyclic redundancy check, a polynomial-division-based checksum for catching accidental data corruption, shown here as 16 hexadecimal characters.

This tool specifically implements CRC-64/XZ (equivalently named CRC-64/GO-ECMA in some references): reflected polynomial 0xc96c5795d7870f42, the same parameters the .xz compression container format uses for its own integrity check.

How CRC64 Calculator Works

Your text is passed to hash-wasm's WebAssembly CRC-64 implementation, which processes it byte by byte through a 64-bit polynomial-division table using the CRC-64/XZ reflected parameters.

The resulting 64-bit remainder is returned as a 16-character hexadecimal string, computed asynchronously since it runs through a WebAssembly module rather than synchronous JavaScript.

When To Use CRC64 Calculator

Use CRC-64 when reproducing or verifying a checksum from a system that specifically uses it, like the .xz compression format, or anywhere a 64-bit checksum space is specifically called for.

For everyday file-integrity checks, CRC-32 remains far more commonly expected (zip, gzip, PNG, Ethernet); reach for CRC-64 specifically when matching an xz-style system or when the larger checksum space is a stated requirement.

Often used alongside CRC32 Calculator, CRC16 Calculator and CRC8 Calculator.

Features

Advantages

Dramatically lower collision probability than CRC-32 thanks to its 64-bit output space.
Matches a real, widely deployed format (xz) exactly, so there's a concrete standard to verify against.
Still vastly cheaper to compute than a cryptographic hash, appropriate for accidental-corruption checking at scale.

Limitations

Like every CRC, offers no resistance to deliberate tampering, only accidental-error detection.
The only CRC tool in this category that's asynchronous (WebAssembly-backed), so it behaves slightly differently from the synchronous CRC-8/16/24/32 tools.
Multiple named 64-bit CRC parameter sets exist (CRC-64/XZ vs. others); confirm which one a target system expects before assuming a match.

Examples

Hashing the standard CRC check string

Input

123456789

Output

995dc9bbdf1939fa

The official CRC-64/XZ check value for the ASCII string "123456789", the standard sanity-check input used across the reveng CRC catalogue, confirmed by directly running hash-wasm's crc64() function.

Hashing a short greeting

Input

Hello, world!

Output

8e59e143665877c4

13 bytes of UTF-8 text reduced to the 16-character CRC-64/XZ checksum, independently computed by running hash-wasm's crc64() function directly rather than looked up.

Best Practices & Notes

Best Practices

Confirm a target system actually uses CRC-64/XZ specifically before assuming this tool's output will match; other 64-bit CRC parameter sets exist and produce different results.
Give the tool a brief moment on first use since the WebAssembly module needs to load before the first digest returns.
For everyday file checksums without a specific 64-bit requirement, CRC-32 remains the more broadly recognized default.

Developer Notes

Delegates to hash-wasm's crc64() function with its default polynomial 0xc96c5795d7870f42 (CRC-64/XZ), the same reason and pattern as this category's Whirlpool tool: a from-scratch 64-bit CRC table in JavaScript risks subtle bitwise correctness bugs that an audited WASM implementation avoids. Verified against the official CRC-64/XZ check value for "123456789" (0x995dc9bbdf1939fa, matching the reveng CRC catalogue) plus an independently computed vector for "Hello, world!" obtained by running hash-wasm's crc64() directly.

CRC64 Calculator Use Cases

Reproducing an xz-compatible CRC-64 checksum by hand
Verifying a CRC-64/XZ implementation against the standard reveng check value
Comparing collision-resistance intuition between CRC-32 and CRC-64 for large-scale checksumming
Teaching how larger CRC output sizes push out the birthday-bound collision risk

Common Mistakes

Assuming any 64-bit CRC output will match this tool without confirming it also uses the CRC-64/XZ polynomial and reflection settings.
Treating a matching CRC-64 as a security guarantee rather than accidental-corruption detection.
Expecting instant output on first use, the WebAssembly module needs a brief moment to load before the first result appears.

Tips

If your target checksum doesn't match, check whether the source system uses a different named CRC-64 variant (the reveng catalogue lists several).
For the far more common 32-bit checksum used by zip/gzip/PNG, use this category's CRC32 Calculator instead.

CRC64 Calculator