JSON array align

json-array-align · version 1.0.0 · JSON & JSONL · free, no key needed

Align two JSON arrays with duplicate-safe occurrence pairs and deterministic LCS tie-breaking.

Use when you need to: align two JSON arrays · find common JSON array sequence · match duplicate array occurrences.

Decide before calling

Read the versioned contract and the supported scope below. Reuse json-array-align@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 json-array-align@1.0.0 for align two JSON arrays. 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

align two JSON arrays
find common JSON array sequence
match duplicate array occurrences
compute deterministic array LCS
map array indexes by value
compare ordered JSON values

Not supported

merging JSON objects by key
reading JSON text or files

Behavior

Values are compared by RFC 8259 JSON structure with object member names sorted; array order and number spelling after parsing follow JavaScript JSON values.
Alignment uses longest common subsequence; on equal alternatives it advances the first input, a deterministic deletion-before-insertion tie rule. Duplicate values are identified by matched occurrence, never by value alone.
The implementation is synchronous, offline and deterministic and reports RFC 8259 + Myers 1986 and version 1.0.0.

Input

left (array of any JSON value, required): max items 128
right (array of any JSON value, required): max items 128

Output

reference (constant "RFC 8259 + Myers 1986", required)
version (constant "1.0.0", required)
pairs (array of object, required): max items 128
left_only (array of integer, required): max items 128; each min 0; each max 127
right_only (array of integer, required): max items 128; each min 0; each max 127

Limits

max input bytes: 65536
max items: 128
max iterations: 49152
max output bytes: 131072

Example

Request input:

{
  "left": [
    "a",
    "b"
  ],
  "right": [
    "a",
    "c",
    "b"
  ]
}

Response:

{
  "result": {
    "reference": "RFC 8259 + Myers 1986",
    "version": "1.0.0",
    "pairs": [
      {
        "left_index": 0,
        "right_index": 0,
        "occurrence": 1
      },
      {
        "left_index": 1,
        "right_index": 2,
        "occurrence": 1
      }
    ],
    "left_only": [],
    "right_only": [
      1
    ]
  }
}

How to call it

MCP

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

{
  "id": "json-array-align",
  "version": "1.0.0",
  "input": {
    "left": [
      "a",
      "b"
    ],
    "right": [
      "a",
      "c",
      "b"
    ]
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/json-array-align/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"left":["a","b"],"right":["a","c","b"]}'

The machine-readable contract is at /v1/tools/json-array-align/versions/1.0.0.

CLI

node cli.mjs run json-array-align 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

JSON array three way merge: Merge base, left and right JSON arrays, returning deterministic output and explicit conflicting edit regions.
JSON keyed array merge: Three-way merge JSON arrays by a JSON Pointer key, returning edits, moves, inserts, deletes, and conflicts.
JSON schema valid items filter: Keep only the JSON records that pass (or fail) one Draft 2020-12 subset schema; returns kept records and index lists.
JSON array anti join: Anti join two JSON arrays of objects on exact keys.
JSON array count: Count structural occurrences in a JSON array in first-seen order.
JSON array filter equals: Filter JSON array objects where a key equals a specific value.