ForHosting KIT · Developer Utilities

CRC-8 checksum calculator

The nine characters 123456789 give the CRC-8 value f4, or 244 in decimal, the documented check for the SMBus profile with polynomial 07, so you can verify a bus frame or a textbook exercise. Paste any text to get its one-byte checksum. Free in your browser.

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Run — free How it works & API

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Worked example

If you enter

Text: 123456789

You get

Result: f4
Crc8: f4
Hex: f4
Decimal: 244

CRC-8 is an eight-bit cyclic redundancy check used in embedded buses, simple framing protocols, and teaching materials that need a compact integrity byte rather than a full cryptographic hash. Engineers, students, and support teams often need the same textbook result for a short string: the standard polynomial 0x07 (x to the eight plus x squared plus x plus one), initial register zero, no bit reflection, and zero final XOR—exactly the CRC-8/SMBus profile whose check value for the ASCII digits one through nine is hexadecimal F4. This CRC-8 checksum tool accepts non-empty text, encodes it as UTF-8, runs that deterministic shift-and-XOR loop, and returns the single checksum byte as two lowercase hexadecimal digits together with the decimal value and a short summary.

What CRC-8 with polynomial 0x07 computes and why the hex byte matters

A cyclic redundancy check treats a message as a polynomial over the Galois field of two elements and divides it by a fixed generator polynomial, leaving a remainder that becomes the checksum. For CRC-8 the remainder is only eight bits wide, so the entire result fits in one byte and is naturally written as two hexadecimal digits. The standard generator used by SMBus, many ATM HEC-style examples, and most online CRC-8 demos is 0x07, which expands to x to the eighth plus x squared plus x plus one.

In software the division is performed by exclusive-oring each input byte into an eight-bit register and shifting left eight times, exclusive-oring the generator whenever the high bit is set. This landing always uses that non-reflected algorithm with initial value zero and final XOR zero, which is the profile whose documented check value for the nine-byte ASCII string one two three four five six seven eight nine is F4.

The response also echoes the decimal integer, the polynomial string 0x07, the algorithm label CRC-8, the UTF-8 byte count, and the original text so clients can display a full audit line without re-deriving metadata. Because CRC-8 is not collision-resistant and not keyed, treat it as a framing or accidental-corruption check, not as proof of authenticity; prefer SHA-family digests when the search intent is cryptographic hashing rather than a one-byte CRC.

Where a one-byte CRC-8 check makes sense

Firmware authors and bus protocol students use a CRC-8 checksum calculator to verify hand-computed remainders against the SMBus-style polynomial without writing a shift loop in every language. Teaching platforms and LMS plugins need a deterministic oracle that rejects empty input instead of returning zero for the empty message, so auto-graders can distinguish missing answers from a real checksum of zero. Content sites ranking for CRC-8 checksum or CRC8 calculator benefit from a live tool whose free path matches the paid automation path byte-for-byte on the same pure module.

Validation failures never consume balance after rejection. Pair with CRC-32 or cryptographic hash landings only when the search intent moves beyond an eight-bit framing check—keep this page focused on standard poly 0x07 CRC-8 so SEO intent stays sharp.

What you can do with it

Classroom CRC remainder demos

Teachers show the classic 123456789 → F4 check value and let students recompute other short strings without installing a CRC library.

FAQ

Which CRC-8 polynomial does this tool use?

The standard poly 0x07 (CRC-8/SMBus): init 0x00, no reflection, xorout 0x00. The documented check for ASCII 123456789 is F4.

What happens if the text is empty?

A non-empty string is required; empty input is not treated as a successful zero checksum.

Is the CRC-8 checksum calculator free?

The browser tool runs free on your device.

Is CRC-8 a cryptographic hash?

No. CRC-8 is an eight-bit integrity check for framing and accidental corruption. Use SHA-256 or similar when you need collision resistance or authentication.

Where is this CRC-8 profile used?

The polynomial 07 with a zero start is the generator used by SMBus, many ATM header-check examples and most online CRC-8 demos. It suits embedded buses, simple framing protocols and teaching material that need a compact integrity byte.

Related tools

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/enc/crc8

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/enc/crc8 \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"text":"123456789"}'

const res = await fetch("https://api.kit.forhosting.com/enc/crc8", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "text": "123456789"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/enc/crc8",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "text": "123456789"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/enc/crc8", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"text":"123456789"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"text":"123456789"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/enc/crc8", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "text": "123456789"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "enc.crc8",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Technical notes

Empty input is rejected with invalid_input so callers never confuse a missing field with a real zero checksum.

Input contract, empty-string errors, and the JSON response shape

The string is encoded as UTF-8 before the CRC loop, so multi-byte characters contribute every code unit byte exactly as an embedded device would if it received the same UTF-8 stream. Pin both a success path and an empty-input error in continuous integration so accidental poly or init changes cannot ship unnoticed. Optional null fields are omitted rather than emitted as null, matching the declarative renderer contract for clean web forms. POST a JSON body with a single required string field named text: any non-empty sequence of characters you want to checksum. Aliases input, value, s, data, message, and payload are accepted for the same field so SDK stubs and form posts stay flexible. Missing text, a non-string value, or an empty string all fail with invalid_input and a clear message that a non-empty string is required; those failures are not billed on the prepaid API. On success the body includes result, crc8, and hex all set to the same two-digit lowercase hexadecimal checksum; decimal set to the integer zero through two hundred fifty-five; polynomial fixed at 0x07; algorithm fixed at CRC-8; input_bytes equal to the UTF-8 length; text echoing the input; and message summarizing the byte count and hex result.

Where a CRC-8 checksum API earns its keep and how pricing works

Call the free in-browser tool for one-off checks; call the prepaid KIT API from backends, serverless functions, and SDKs when you need a stable contract under balance at $0.002 per successful item. Keep payloads to ordinary text sizes appropriate for a Worker isolate item call; this tool is for short strings and protocol snippets, not multi-megabyte binary blobs.

Integration use cases

SMBus and embedded protocol checks

Verify that a payload string produces the expected one-byte CRC-8 trailer under poly 0x07 before comparing device logs or unit-test vectors.

CI fixtures for framing code

Pipelines pin deterministic CRC-8 hex outputs and the empty-input error so accidental poly or init changes fail fast.

Technical questions

How do I compute a CRC-8 checksum of text?

Send JSON with a non-empty string field text. The API UTF-8-encodes the string, runs CRC-8 with polynomial 0x07, and returns the byte as two lowercase hex digits in result, crc8, and hex.

Read the full KIT documentation →

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