CSV row diff

csv-row-diff · version 1.0.0 · CSV & tables · free, no key needed

Compare two CSV documents with identical headers by unique key tuples and report added, removed, and changed rows.

Use when you need to: csv row diff · diff csv rows by keys · compare keyed csv rows.

Supported

• csv row diff
• diff csv rows by keys
• compare keyed csv rows

Not supported

• outer join
• fuzzy matching
• numeric comparison
• case-insensitive diff
• unkeyed row diff
• read files
• fetch urls

Behavior

• left and right must share identical headers in the same order.
• keys is a non-empty unique subset of those headers, at most 32 names.
• Duplicate key tuples on either side are rejected because the diff is undefined.
• Rows are classified by exact key-tuple membership and exact remaining-column string tuples.
• added contains right-only keys in right row order; removed and changed follow first-seen left key order.
• changed rows are the right-side (new) values with the original headers; no change column is added.
• No trimming, case folding, type coercion, or numeric comparison is performed.
• Empty documents without headers are rejected; header-only inputs emit the shared header and zero counts.
• The first header name may not begin with U+FEFF because it is ambiguous with a CSV byte-order mark.

Input

• left (string, required): max length 256000
• right (string, required): max length 256000
• keys (array of string, required): min items 1; max items 32; each min length 1

Output

• added (string, required)
• removed (string, required)
• changed (string, required)
• counts (object, required)

Limits

• max input bytes: 256000
• max data rows: 5000
• max columns: 256
• max header name bytes: 256
• max keys: 32
• max output bytes: 1048576

Example

Request input:

{
  "left": "id,name,city\n1,Ada,London\n2,Lin,Paris\n3,Zoe,Berlin\n",
  "right": "id,name,city\n1,Ada,London\n2,Lin,Rome\n4,Bob,Oslo\n",
  "keys": [
    "id"
  ]
}

Response:

{
  "result": {
    "added": "id,name,city\n4,Bob,Oslo\n",
    "removed": "id,name,city\n3,Zoe,Berlin\n",
    "changed": "id,name,city\n2,Lin,Rome\n",
    "counts": {
      "added": 1,
      "removed": 1,
      "changed": 1,
      "unchanged": 1
    }
  }
}

How to call it

MCP

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

{
  "id": "csv-row-diff",
  "version": "1.0.0",
  "input": {
    "left": "id,name,city\n1,Ada,London\n2,Lin,Paris\n3,Zoe,Berlin\n",
    "right": "id,name,city\n1,Ada,London\n2,Lin,Rome\n4,Bob,Oslo\n",
    "keys": [
      "id"
    ]
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/csv-row-diff/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"left":"id,name,city\n1,Ada,London\n2,Lin,Paris\n3,Zoe,Berlin\n","right":"id,name,city\n1,Ada,London\n2,Lin,Rome\n4,Bob,Oslo\n","keys":["id"]}'

The machine-readable contract is at /v1/tools/csv-row-diff/versions/1.0.0.

CLI

node cli.mjs run csv-row-diff 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• CSV reconcile: Reconcile two CSV documents by key columns, reporting full population totals and bounded samples for added, removed, changed, invalid-key, and ambiguous rows.
• CSV add row number: Prepend a 1-based row_number column of canonical integer strings.
• CSV anti join: Keep left CSV rows whose exact key tuples do not appear in the right document.
• CSV dedupe: Remove duplicate CSV data rows while preserving the first occurrence.
• CSV group count: Count CSV rows by exact named-column tuples in first-seen order.
• CSV slice rows: Take a contiguous window of CSV data rows by offset and limit, keeping the header.