SmartQueryTools

Pad Column in JSON Files Online

Left-pad or right-pad a column in JSON files to a fixed width directly in your browser. Zero-pad numeric codes, pad product IDs to a fixed length, or right-pad text fields — no upload required.

How to pad Column in JSON files

  1. Drop your file onto the upload area. The first column is selected by default, and the first 200 rows are shown.
  2. Pick the column to pad and the pad side: Left pad (lpad, for 007) or Right pad (rpad, for 700).
  3. Set the total width in characters (1 to 200, default 10) and the pad character (one character, default 0). A live hint shows what "42" would become.
  4. Choose "Replace column in place", or "Append as new column" with a name (default: the column name plus _padded).
  5. Click Pad Column, check the preview, and download the 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 retail store list was opened and saved in a spreadsheet, which turned US ZIP codes into numbers and dropped their leading zeros. The ZIPs must be five characters again before the file is matched against a postal database.

Input (JSON)

[
  {
    "store_id": "S-014",
    "city": "Boston",
    "zip": 2134
  },
  {
    "store_id": "S-022",
    "city": "Jersey City",
    "zip": 7302
  },
  {
    "store_id": "S-031",
    "city": "San Francisco",
    "zip": 94107
  },
  {
    "store_id": "S-047",
    "city": "Holtsville",
    "zip": 501
  }
]

Settings

  • Column to pad: zip
  • Pad side: Left pad
  • Total width: 5
  • Pad character: 0
  • Output mode: Replace column in place

Result

store_idcityzip
S-014Boston02134
S-022Jersey City07302
S-031San Francisco94107
S-047Holtsville00501

Each ZIP is converted to text and zeros are added on the left until it is five characters long. 94107 is already five characters and is unchanged. The zip column is now text, not a number, which is what keeps the zeros. A value longer than five characters, such as a ZIP+4 written as 021341234, would be cut to its first five characters.

Working with JSON files

In the output JSON the padded field is a string: "zip": 2134 becomes "zip": "02134". This is often the whole point, because a JSON number cannot hold leading zeros at all. APIs that validate the field as a string of a fixed length will accept the padded value without further conversion. Decimal numbers keep their decimal point when converted, so 12.5 padded to width 6 with zeros gives "0012.5", which is rarely a useful code. Pad integer keys such as account numbers, SKUs or check numbers, and leave measurements as numbers.

Booleans are padded as the text true or false, and nested objects are rendered as text before padding, so pick a top-level scalar key. Objects with a missing or null value stay null after padding and are not filled with pad characters. Width counts characters, not bytes, so "é" is one character and accented names pad to the expected visual length.

Frequently Asked Questions

Does padding turn JSON numbers into strings?

Yes. The padded key is always a JSON string, since a number cannot keep leading zeros. Other keys keep their original types.

What happens to null values in JSON when padding?

They stay null. Padding is only applied to values that exist, so missing keys are not turned into strings of zeros.

What happens to values longer than the target width?

They are cut to the width. With a width of 5, "123456" becomes "12345" whether you pad left or right. Check the longest value in the column before choosing the width.

Can I pad with more than one character, such as "ab"?

No. The pad character box accepts a single character. An empty box falls back to 0.

Is the padded column still a number?

No. Padding converts the value to text first, so the result is always a text column. That is what lets it keep leading zeros.

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