Add Row Numbers to JSON Files Online

Add a row number index column to JSON files directly in your browser. Set the column name and starting number — no upload required.

How to add Row Numbers to JSON files

Drop your file onto the upload area. The row count is shown and the first 200 rows are previewed.
Type a name for the new column. It defaults to row_number.
Set Start at to the first number you want. It defaults to 1, and 0 or a negative number also works.
Click Add Row Numbers. The new column appears as the first column in the preview.
Click Download to save the numbered file in the same format you uploaded.

Your file is processed locally in your browser and is never uploaded. The free limit is 50 MB per file; larger files work if your device has the memory for them.

Worked example

A research team has a batch of survey responses and a second batch already numbered up to 100. They want the new batch to carry on from 101 so the two can be combined later.

Input (JSON)

[
  {
    "respondent": "r_8f2a",
    "country": "Ireland",
    "score": 7,
    "completed": true
  },
  {
    "respondent": "r_03cd",
    "country": "Portugal",
    "score": 9,
    "completed": true
  },
  {
    "respondent": "r_b771",
    "country": "Ireland",
    "score": null,
    "completed": false
  },
  {
    "respondent": "r_5e10",
    "country": "Canada",
    "score": 6,
    "completed": true
  }
]

Settings

Column name: response_no
Start at: 101

Result

response_no	respondent	country	score	completed
101	r_8f2a	Ireland	7	true
102	r_03cd	Portugal	9	true
103	r_b771	Ireland	NULL	false
104	r_5e10	Canada	6	true

A new integer column called response_no is placed in front of the existing columns and counts up by one per row from 101. Numbers follow the order of the rows in the file. The other columns are unchanged, including the missing score for r_b771.

Working with JSON files

Each object in the JSON array gets a new key holding its position. The new key is written first in every object, followed by the original keys. The value is a JSON number, not a string, so {"row_number": 1, ...} rather than "1".

Because the file passes through a table, every object in the output has the same set of keys. Keys missing from an object in the source are written with null. Objects with nested values keep them as nested JSON. If your records already have an id key, choose a different name such as seq or position for the new one so the two are easy to tell apart. Numbering follows array order. This helps before sending records to a system that may reorder them. Each object carries its original position, so you can match responses back to the source. Key names are case-sensitive in JSON, so Row_Number and row_number would be two separate keys.

Frequently Asked Questions

Is the row number added as a number or a string in JSON?

As a number. Each object gets a numeric value, such as "row_number": 42.

Where does the new key appear in each JSON object?

It is the first key in every object, before the original keys.

Can I start numbering at 0?

Yes. Set Start at to 0 for zero-based indexes. Any whole number works, including negatives. An empty box or a value that is not a number uses the default of 1, and decimals are cut to a whole number.

In what order are rows numbered?

In the order they appear in the file. The tool does not sort. Sort the file first if you want numbers to follow a date or ID column.

What if I leave the column name blank?

The column is named row_number. Choose a name that is not already used by a column in your file.

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