CRC16 Checksum Generator

Q: Is my text or file uploaded anywhere?

No. The CRC-16 digest is computed by JavaScript in this tab, and an imported file is read locally with the browser's File API. Nothing leaves your machine, which is why it is safe to hash configuration files or internal data here.

Q: Why does another tool give me a different CRC-16 for the same text?

Because the bytes differ, even if the text looks identical. The usual culprits are a trailing newline (most command-line tools add one when you echo), CRLF versus LF line endings, a byte-order mark, or a different text encoding. This tool hashes exactly what is in the box, encoded as UTF-8, and points out line endings and BOMs when it sees them.

Q: Which CRC-16 does Modbus use?

Modbus RTU uses CRC-16/MODBUS: polynomial 0x8005 reflected, initial value 0xFFFF, no final XOR. Note that Modbus transmits the CRC low byte first, so the bytes on the wire are swapped relative to the hex shown here.

Q: What is the difference between CCITT-FALSE and XMODEM?

Both use polynomial 0x1021 without bit reflection. CCITT-FALSE starts from 0xFFFF and XMODEM starts from 0x0000. That one setting is enough to make every checksum different.

Q: Why are there so many CRC-16 variants?

Different standards bodies picked parameters independently over decades. A CRC catalogue lists more than twenty 16-bit variants; the ones here cover Modbus, XMODEM, many serial protocols and the common ARC/IBM form.

Calculate CRC-16 checksums of text or files in your browser — ARC, MODBUS, CCITT-FALSE and XMODEM variants.

Text to hash (0 bytes)

Output Variant Hash each line separately

Digest

Compare against a published checksum (optional)

What It Does

This tool calculates 16-bit CRC checksums. CRC-16 is not one algorithm but a family of parameter sets — polynomial, initial value, bit reflection — and two devices only agree if they use the same one. The page offers the four that cover most real protocols: CRC-16/ARC, CRC-16/MODBUS, CRC-16/CCITT-FALSE and CRC-16/XMODEM, each verified against its catalogued check value.

When to Use It

You are writing a Modbus RTU frame and need the CRC to append.
A serial device's datasheet specifies CCITT or XMODEM CRC and your values do not match.
You are sending a file over XMODEM and want to confirm a block's CRC.
You have a CRC from a capture and want to find which variant produced it.

Worked Examples

123456789

The universal check string. ARC gives bb3d, MODBUS 4b37, CCITT-FALSE 29b1 and XMODEM 31c3 — switch the variant to see each.

With empty input the CRC is simply the variant's initial value after its final steps: 0000 for ARC and XMODEM, ffff for MODBUS and CCITT-FALSE.

Hello

Change the variant and every value differs. If your device disagrees, the variant is almost always the reason.

Features

CRC-16 digest as you type

Hash files as raw bytes without uploading

Hex / HEX / Base64 output

Hash each line separately

Checksum comparison that recognises the wrong algorithm

Warnings for line endings

BOMs and passwords

How to Use

1. Type or paste text, or choose Hash a file to hash a file's raw bytes. 2. Pick the output encoding the value will be compared against — hex is the usual one. 3. To check a published checksum, paste it into the comparison box; the tool tells you whether it matches and, if not, whether it is even the same algorithm.

Common Mistakes

Hashing text that is not byte-for-byte what the other side hashed. A trailing newline, Windows line endings or a byte-order mark each produce a completely different CRC-16 value, and none of them are visible.
Comparing a hex digest with a Base64 one. They encode the same bytes differently, so they never look alike even when they match — switch the output format before deciding two values disagree.
Comparing digests in mixed case and concluding they differ. Hex is case-insensitive; ABCDEF and abcdef are the same value.
Using a plain CRC-16 digest where a secret is involved. To prove a message came from someone holding a key, you need HMAC, not hash(secret + message).

Frequently Asked Questions

Is my text or file uploaded anywhere?

Why does another tool give me a different CRC-16 for the same text?

Which CRC-16 does Modbus use?

What is the difference between CCITT-FALSE and XMODEM?

Why are there so many CRC-16 variants?

Everything runs in your browser. Text and files are hashed locally — nothing is uploaded, logged or stored.