JSON array left join

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

Left join two JSON arrays of objects on exact keys.

Use when you need to: json array left join · left join json arrays · left join json objects on keys.

Supported

• json array left join
• left join json arrays
• left join json objects on keys

Not supported

• outer join
• fuzzy keys

Behavior

• Matches objects from the left and right arrays based on strict equality of the specified keys.
• Returns a new array containing the cartesian product of all matching rows.
• If a left row has no matches, it is included in the output once with only its original properties.
• Output array is ordered first by the left array's order, then by the right array's order.
• If a row is missing any of the join keys, it is treated as having no match (missing keys never match each other).
• A key tuple with more than 64 rows on either side is rejected.

Input

• left (array of object, required): max items 10000
• right (array of object, required): max items 10000
• keys (array of string, required): min items 1; max items 32; each min length 1

Output

• result (array of object, required)
• count (integer, required)

Limits

• max array items: 10000
• max output items: 10000
• max keys: 32
• max join duplicates: 64

Example

Request input:

{
  "left": [
    {
      "id": 1,
      "name": "Alice"
    },
    {
      "id": 2,
      "name": "Bob"
    }
  ],
  "right": [
    {
      "id": 1,
      "role": "Admin"
    }
  ],
  "keys": [
    "id"
  ]
}

Response:

{
  "result": {
    "result": [
      {
        "id": 1,
        "name": "Alice",
        "role": "Admin"
      },
      {
        "id": 2,
        "name": "Bob"
      }
    ],
    "count": 2
  }
}

How to call it

MCP

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

{
  "id": "json-array-left-join",
  "version": "1.0.0",
  "input": {
    "left": [
      {
        "id": 1,
        "name": "Alice"
      },
      {
        "id": 2,
        "name": "Bob"
      }
    ],
    "right": [
      {
        "id": 1,
        "role": "Admin"
      }
    ],
    "keys": [
      "id"
    ]
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/json-array-left-join/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"left":[{"id":1,"name":"Alice"},{"id":2,"name":"Bob"}],"right":[{"id":1,"role":"Admin"}],"keys":["id"]}'

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

CLI

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

Get the client at /clients/cli/.

Related tools

• JSON array inner join: Inner join two JSON arrays of objects on exact keys.
• JSON array anti join: Anti join two JSON arrays of objects on exact keys.
• JSON array group by: Group an array of JSON objects by exact keys.
• JSON array sort objects: Stably sort an array of objects by explicit string keys using UTF-16 lexicographic order.
• JSON array concat: Concatenate multiple JSON arrays of objects into one.
• JSON array distinct by: Deduplicate a JSON array of objects based on specific keys.