Permutation indices check

permutation-indices-check · version 1.0.0 · Numbers & math · free, no key needed

Check whether claimed indices are exactly one occurrence of every source index, reporting the first discrepancy.

Use when you need to: check index permutation · validate claimed permutation indices · detect duplicate permutation index.

Decide before calling

Read the versioned contract and the supported scope below. Reuse permutation-indices-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 permutation-indices-check@1.0.0 for check index permutation. 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 index permutation
• validate claimed permutation indices
• detect duplicate permutation index
• find first missing permutation index
• verify index rearrangement
• audit permutation certificate

Not supported

• compute a sorting permutation
• repair invalid indices

Behavior

• A valid claim contains each source index exactly once.
• Claim positions are scanned left to right; then missing source indices are scanned ascending.
• Source scalars, including null and duplicates, affect only the required length.
• The claim is never repaired or replaced.

Input

• source (array of string or number or boolean or null, required): max items 4096
• claimed_indices (array of integer, required): max items 4096; each min 0; each max 4096

Output

• valid (boolean, required)
• reason (string or null, required)
• discrepancy (object or null, required)
• reference_version (constant "Knuth TAOCP Vol. 1, 3rd ed., §1.2.5 (Permutations); ECMA-262 2026 §7.2.11 SameValueZero", required)

Limits

• max items: 4096
• max input bytes: 262144
• max output bytes: 1024

Example

Request input:

{
  "source": [
    "a",
    "b",
    "c"
  ],
  "claimed_indices": [
    2,
    0,
    1
  ]
}

Response:

{
  "result": {
    "valid": true,
    "reason": null,
    "discrepancy": null,
    "reference_version": "Knuth TAOCP Vol. 1, 3rd ed., §1.2.5 (Permutations); ECMA-262 2026 §7.2.11 SameValueZero"
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "permutation-indices-check",
  "version": "1.0.0",
  "input": {
    "source": [
      "a",
      "b",
      "c"
    ],
    "claimed_indices": [
      2,
      0,
      1
    ]
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/permutation-indices-check/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"source":["a","b","c"],"claimed_indices":[2,0,1]}'

The machine-readable contract is at /v1/tools/permutation-indices-check/versions/1.0.0.

CLI

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

Get the client at /clients/cli/.

Related tools

• Join inner result check: Check a claimed ordered inner join index result and report its first discrepancy.
• Join left result check: Check a claimed ordered left join index result and report its first discrepancy.
• Join semi result check: Check a claimed ordered semi-join index result and report its first discrepancy.
• Permutation values check: Check whether claimed values are a SameValueZero multiset permutation, reporting the first source-order discrepancy.
• Permutation ranked check: Check exact stable ordinal ranks for decimal-string values and nulls, reporting the first source-index discrepancy.
• Precedence order check: Check whether a claimed node order is exactly a precedence-respecting linear extension of a caller-supplied DAG.