# Hex bytes concat

`hex-bytes-concat` · version 1.0.0 · Encoding & checksums · free, no key needed

Concatenate a bounded ordered list of lowercase hex byte strings into one hex string.

**Use when you need to: hex bytes concat · concatenate hex byte strings · join hex byte parts.**

## Supported

- hex bytes concat
- concatenate hex byte strings
- join hex byte parts

## Not supported

- uppercase hex
- 0x prefix
- byte separators
- insert delimiter between parts
- flatten nested arrays
- decode hex to text

## Behavior

- parts is an ordered array of lowercase hex byte strings: 0-9 and a-f only, two hex digits per byte, no 0x prefix, no separators, no whitespace, no uppercase.
- parts has at most 1000 items.
- Each part and the concatenated result are bounded to 128000 bytes (256000 hex characters); exceeding either limit is rejected before the result is built.
- Result hex is every part decoded to bytes and concatenated in array order, then re-encoded as lowercase hex. No delimiter is inserted between parts.
- An empty parts array, and an array containing only empty strings, both produce an empty result.

## Input

- `parts` (array of string, required): max items 1000; each max length 256000

## Output

- `hex` (string, required): max length 256000

## Limits

- max parts: 1000
- max input bytes per part: 128000
- max output bytes: 128000

## Example

Request input:

```json
{
  "parts": [
    "ab",
    "cd",
    "ef"
  ]
}
```

Response:

```json
{
  "result": {
    "hex": "abcdef"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "hex-bytes-concat",
  "version": "1.0.0",
  "input": {
    "parts": [
      "ab",
      "cd",
      "ef"
    ]
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/hex-bytes-concat/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"parts":["ab","cd","ef"]}'
```

The machine-readable contract is at [/v1/tools/hex-bytes-concat/versions/1.0.0](/v1/tools/hex-bytes-concat/versions/1.0.0).

### CLI

```sh
node cli.mjs run hex-bytes-concat 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [Hex bytes xor](/tools/hex-bytes-xor): Byte-wise XOR of two equal-length lowercase hex byte strings. Transformation only; no cryptographic security claim.
- [Hex bytes slice](/tools/hex-bytes-slice): Slice a lowercase hex byte string by explicit byte-index bounds, half-open like Array.slice.
- [UTF-8 hex](/tools/utf8-hex): Encode a Unicode string as lowercase hex of its UTF-8 bytes. Transformation only; no security claim.
- [Adler-32](/tools/adler32): Adler-32 of UTF-8 bytes (RFC 1950). Integrity check only; no security claim.
- [Base64 UTF-8](/tools/base64-utf8): Decode standard Base64 to UTF-8 text. Transformation only; no security claim.
- [CRC-32](/tools/crc32): CRC-32 of UTF-8 bytes (ISO 3309 / ZIP / PNG polynomial). Integrity check only; no security claim.