Regex replacement check

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

Checks an exact claimed bounded regex replacement and reports the first differing UTF-16 index.

Use when you need to: check regex replacement claim · validate replaced text · compare regex substitution.

Decide before calling

Read the versioned contract and the supported scope below. Reuse regex-replacement-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-replacement-check@1.0.0 for check regex replacement 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 replacement claim
• validate replaced text
• compare regex substitution
• verify replacement output
• find first replacement mismatch
• check dollar replacement tokens

Not supported

• execute arbitrary regular expressions
• repair an incorrect replacement

Behavior

• Patterns use the documented RE2-compatible linear subset; indices are ECMA-262 UTF-16 indices.
• Replacement tokens $$, $&, $`, and $' follow ECMA-262 replacement substitution; other dollar forms are literal.
• Replacement construction stops before the declared UTF-8 result-size bound is crossed; discrepancy values are complete Unicode scalar values containing the differing code unit.

Input

• text (string, required): max length 65536
• pattern (string, required): min length 1; max length 256
• flags (string, required): max length 2
• replacement (string, required): max length 65536
• claimed (string, required): max length 262144

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

Example

Request input:

{
  "text": "a1b2",
  "pattern": "\\d",
  "flags": "",
  "replacement": "X",
  "claimed": "aXbX"
}

Response:

{
  "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), then call execute with:

{
  "id": "regex-replacement-check",
  "version": "1.0.0",
  "input": {
    "text": "a1b2",
    "pattern": "\\d",
    "flags": "",
    "replacement": "X",
    "claimed": "aXbX"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/regex-replacement-check/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"text":"a1b2","pattern":"\\d","flags":"","replacement":"X","claimed":"aXbX"}'

The machine-readable contract is at /v1/tools/regex-replacement-check/versions/1.0.0.

CLI

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

Get the client at /clients/cli/.

Related tools

• Regex tokenization check: Checks claimed regex token texts and UTF-16 spans, returning the first mismatching token.
• Regex split check: Checks claimed regex split parts and separator boundaries in deterministic source order.
• Dedupe first check: Check an exact first-wins SameValueZero deduplication claim and report its first discrepancy.
• Dedupe keyed check: Check an exact keyed Map deduplication claim and report its first discrepancy.
• Dedupe last check: Check an exact last-wins SameValueZero deduplication claim and report its first discrepancy.
• Join inner result check: Check a claimed ordered inner join index result and report its first discrepancy.