Is Adler-32 the same as CRC32?

No, they solve the same broad problem (fast accidental-corruption detection) with different math. Adler-32 sums byte values into two running totals modulo a prime (65521) and combines them, which is cheaper to compute in software than CRC32's polynomial division, but it's measurably weaker at catching certain error patterns, especially on very short data, which is part of why Mark Adler himself has noted CRC32 is generally the better choice unless raw computation speed is the deciding factor.

Where is Adler-32 actually used?

Its most common home is the zlib compressed data format (RFC 1950), the wrapper DEFLATE data gets when used outside of gzip, PNG's image data, PDF streams, and various other systems that lean on zlib all carry an Adler-32 checksum as part of that container format.

Is Adler-32 weaker than CRC32 for short inputs?

Yes, this is a well-documented limitation. Adler-32's checksum quality degrades on very short messages (roughly under a few hundred bytes) because one of its two running sums doesn't have enough data to spread across its full value range, weakening its error-detection power exactly in the size range a lot of short strings and small files fall into.

Does this tool send my text to a server?

No. Adler-32 is computed entirely client-side in JavaScript, so nothing you type here is transmitted anywhere.

Adler-32 Calculator - Compute Adler-32 Online

Overview

Introduction

Adler-32 was designed as a faster-to-compute alternative to CRC32 for the same job, accidental-corruption detection, and it's the checksum quietly wrapped around every zlib-compressed data stream.

This tool computes Adler-32's checksum of any text you provide, entirely in your browser, matching the same value zlib, PNG, and PDF tooling would compute.

What Is Adler-32 Calculator?

Adler-32 is a checksum algorithm designed by Mark Adler (co-author of zlib) and specified in RFC 1950, producing a 32-bit result shown here as 8 hexadecimal characters.

It works by maintaining two running sums modulo the prime 65521, one a simple sum of all bytes, the other a sum of the running sums, then packing both into the high and low 16 bits of the final 32-bit checksum.

How Adler-32 Calculator Works

Starting from a = 1 and b = 0, each byte of your UTF-8 encoded text updates a as (a + byte) mod 65521, then updates b as (b + a) mod 65521.

The final checksum packs b into the upper 16 bits and a into the lower 16 bits (result = (b << 16) | a), then that 32-bit value is hex-encoded into the 8-character output.

When To Use Adler-32 Calculator

Use Adler-32 when you're matching or reproducing a value from a zlib-based format (compressed streams, PNG image chunks, PDF streams) that already computes it as part of the container.

For a new, general-purpose accidental-error checksum without that specific compatibility need, CRC32 generally offers better error-detection quality, especially on shorter inputs, at a similar computational cost in most modern software.

Often used alongside CRC32 Calculator and Random Adler32 Hash Generator.

Features

Advantages

Very cheap to compute, simpler arithmetic than CRC32's table-based polynomial division.
Matches the checksum embedded in zlib, PNG, and PDF stream formats exactly.
Sufficient for its intended purpose: catching accidental corruption in compressed data streams.

Limitations

Weaker error-detection quality than CRC32, especially for short inputs, a documented and acknowledged tradeoff of its design.
Not cryptographically secure in any sense; trivial to construct a deliberate collision.
Less universally recognized outside of the zlib/PNG/PDF ecosystem than CRC32.

Examples

Hashing a short greeting

Input

Hello, world!

Output

205e048a

13 bytes of UTF-8 text produce the standard 8-character Adler-32 checksum.

Hashing a well-known reference string

Input

Wikipedia

Output

11e60398

This exact input/output pair is the worked example shown on Wikipedia's own Adler-32 article, useful for confirming any implementation matches the standard.

Best Practices & Notes

Best Practices

Use Adler-32 specifically to match a zlib/PNG/PDF-style checksum, not as a general-purpose default over CRC32.
For new designs without that specific compatibility need, CRC32 is generally the better-tested, better-performing choice for accidental-error detection.
Never rely on Adler-32 (or any checksum in this family) for tamper resistance; it offers none.

Developer Notes

This tool implements Adler-32 exactly per RFC 1950 (modulus 65521, two running sums packed into the high/low 16 bits), verified against the RFC's own worked example and cross-checked against Node's zlib bindings.

Adler-32 Calculator Use Cases

Verifying a zlib-compressed stream, PNG chunk, or PDF stream's embedded checksum
Reproducing a known Adler-32 value while debugging compression-related code
Building a lightweight, fast internal checksum for non-adversarial data
Cross-checking a value against zlib or PNG tooling output

Common Mistakes

Choosing Adler-32 over CRC32 for a new design without needing zlib/PNG/PDF compatibility specifically; CRC32 usually detects errors better, especially on short data.
Using Adler-32 to verify data hasn't been maliciously tampered with; it offers no resistance to a deliberate attacker.
Assuming Adler-32 and CRC32 are interchangeable or related; they use entirely different math and won't match.

Tips

If you're not specifically matching a zlib/PNG/PDF value, the CRC32 tool is usually the better general-purpose accidental-error checksum.
Remember Adler-32's error-detection quality is weaker on short inputs, don't rely on it as strong evidence of correctness for small data.

Adler-32 Calculator