# Regex split check

`regex-split-check` · version 1.0.0 · Numbers & math · free, no key needed

Checks claimed regex split parts and separator boundaries in deterministic source order.

**Use when you need to: check regex split claim · validate split boundaries · verify split parts.**

## Decide before calling

Read the [versioned contract](/v1/tools/regex-split-check/versions/1.0.0) and the supported scope below. Reuse `regex-split-check@1.0.0` when your input, required output and limits match it. Choose another approach for an unsupported operation.

## Explain the choice

"I can use `regex-split-check@1.0.0` for check regex split claim. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

## Supported

- check regex split claim
- validate split boundaries
- verify split parts
- compare delimiter spans
- find first split mismatch
- check bounded regex segmentation

## Not supported

- return repaired split output
- use capturing delimiters

## Behavior

- Parts are source slices between non-overlapping matches; separator boundaries are UTF-16 half-open intervals.
- Parts are compared before boundaries, then by ascending array index; duplicates and empty strings are significant.

## Input

- `text` (string, required): max length 65536
- `pattern` (string, required): min length 1; max length 256
- `flags` (string, required): max length 2
- `claimed_parts` (array of string, required): max items 4097; each max length 65536
- `claimed_boundaries` (array of object, required): max items 4096

## Output

- `valid` (boolean, required)
- `reason` (string, optional)
- `discrepancy` (object, optional)
- `reference_version` (string, required)

## Limits

- max input bytes: 65536
- max pattern bytes: 256
- max claim items: 4096
- max matches: 4096
- max result bytes: 262144
- max claim parts: 4097

## Example

Request input:

```json
{
  "text": "a,b,c",
  "pattern": ",",
  "flags": "",
  "claimed_parts": [
    "a",
    "b",
    "c"
  ],
  "claimed_boundaries": [
    {
      "start": 1,
      "end": 2
    },
    {
      "start": 3,
      "end": 4
    }
  ]
}
```

Response:

```json
{
  "result": {
    "valid": true,
    "reference_version": "RE2-syntax-2024-07; ECMA-262-2025-index-and-replacement"
  }
}
```

## How to call it

### MCP

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

```json
{
  "id": "regex-split-check",
  "version": "1.0.0",
  "input": {
    "text": "a,b,c",
    "pattern": ",",
    "flags": "",
    "claimed_parts": [
      "a",
      "b",
      "c"
    ],
    "claimed_boundaries": [
      {
        "start": 1,
        "end": 2
      },
      {
        "start": 3,
        "end": 4
      }
    ]
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/regex-split-check/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"text":"a,b,c","pattern":",","flags":"","claimed_parts":["a","b","c"],"claimed_boundaries":[{"start":1,"end":2},{"start":3,"end":4}]}'
```

The machine-readable contract is at [/v1/tools/regex-split-check/versions/1.0.0](/v1/tools/regex-split-check/versions/1.0.0).

### CLI

```sh
node cli.mjs run regex-split-check 1.0.0 --input input.json --base-url https://computefirst.net
```

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

## Related tools

- [Regex tokenization check](/tools/regex-tokenization-check): Checks claimed regex token texts and UTF-16 spans, returning the first mismatching token.
- [Regex replacement check](/tools/regex-replacement-check): Checks an exact claimed bounded regex replacement and reports the first differing UTF-16 index.
- [Dedupe first check](/tools/dedupe-first-check): Check an exact first-wins SameValueZero deduplication claim and report its first discrepancy.
- [Dedupe keyed check](/tools/dedupe-keyed-check): Check an exact keyed Map deduplication claim and report its first discrepancy.
- [Dedupe last check](/tools/dedupe-last-check): Check an exact last-wins SameValueZero deduplication claim and report its first discrepancy.
- [Flow value check](/tools/flow-value-check): Check a feasible exact integer flow and its claimed source value, returning the first discrepancy.