Format Timestamps in JSON Files Online

Reformat timestamp and date columns in JSON files directly in your browser. Convert between ISO 8601, Unix epoch, US date, and custom strftime patterns — no upload required.

How to format Timestamps in JSON files

Drop your file onto the upload area. The first 200 rows are shown, and the first date or timestamp column is pre-selected if the file has one.
Pick the column to format. The dropdown shows each column's detected type, and the output column name defaults to the column name plus _formatted.
Choose the input format: Auto-detect for ISO-style text, Unix epoch in seconds or milliseconds, or a custom strptime pattern such as %d/%m/%Y.
Choose the output format: ISO 8601, date only, US date, Unix epoch seconds or milliseconds, or a custom strftime pattern. Then click Format Timestamps.
Check the result preview and download the file. The formatted column replaces the original in the same position.

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 set of temperature sensors logs readings with slightly different timestamp styles, and one device writes "n/a" when its clock has not synced. A US reporting template needs plain MM/DD/YYYY dates.

Input (JSON)

[
  {
    "sensor_id": "S-01",
    "event_time": "2026-04-11 08:15:32",
    "temp_c": 18.4
  },
  {
    "sensor_id": "S-02",
    "event_time": "2026-04-11T23:59:59",
    "temp_c": 17.9
  },
  {
    "sensor_id": "S-01",
    "event_time": "2026-04-12 00:00:05",
    "temp_c": 18.1
  },
  {
    "sensor_id": "S-03",
    "event_time": "n/a",
    "temp_c": 19.2
  }
]

Settings

Column to format: event_time (VARCHAR)
Output column name: event_time_formatted (default)
Input format: Auto-detect
Output format: US date (01/15/2024)

Result

sensor_id	event_time_formatted	temp_c
S-01	04/11/2026	18.4
S-02	04/11/2026	17.9
S-01	04/12/2026	18.1
S-03	NULL	19.2

Auto-detect reads both the space and the T separator as timestamps. The US date output keeps only month, day and year. "n/a" cannot be read as a time, so it becomes empty rather than stopping the run. The original event_time column is replaced by event_time_formatted in the same position, so keep a copy if you need both.

Working with JSON files

JSON has no date type, so timestamps are strings. Date-only strings such as "2026-04-11" are usually typed as DATE when the file loads, while full timestamp strings often stay as text. Auto-detect converts both. Strings with a zone offset, such as "2026-04-11T08:15:32+02:00", are converted to UTC and the offset is dropped, giving 06:15:32. Strings without an offset are kept as written. Numeric fields such as "created": 1775895332 load as integers and can be read with the epoch seconds or epoch milliseconds input option.

Timestamps inside nested objects are not listed in the column picker, which only shows top-level keys. Flatten the JSON first so a field like meta.created_at becomes its own column. The formatted field is written back as a string, or as a number for epoch outputs, under the new key name. Empty results are written as null, so objects where the timestamp could not be read keep the key with a null value.

Frequently Asked Questions

How do I convert Unix timestamps in a JSON file to dates?

Select the numeric field, choose Unix epoch seconds or milliseconds as the input format, then choose ISO 8601 or date only as the output. The result is written as a string field.

Can I format a timestamp that sits inside a nested JSON object?

Not directly. Only top-level keys appear in the picker. Run Flatten JSON first so the nested field becomes a column, then format it.

What happens to values that cannot be read as a timestamp?

With Auto-detect they become empty (NULL) and the rest of the column is converted. With a custom strptime pattern, any value that does not fit the pattern stops the run with an error, so the file is not half converted.

Does the tool keep the original column?

No. The formatted column replaces the original in the same position, under the output column name you set. Keep your original file if you need both versions.

Which time zone are the results in?

UTC, whatever time zone your computer uses. Epoch seconds and epoch milliseconds are both read as UTC. In Auto-detect, a value with an offset or Z, such as 2026-04-11T08:15:32+02:00, is converted to UTC. A value without an offset is kept exactly as written.

Is there a European DD/MM/YYYY output option?

Not as a preset. Choose Custom pattern (strftime) as the output and enter %d/%m/%Y. The same field takes any strftime tokens, such as %d %b %Y for 11 Apr 2026.

Related Tools

Truncate Dates in JSON Files Online

Truncate date and timestamp columns in JSON files to a chosen precision — year, quarter, month, week, day, hour, or minute — directly in your browser. Rounds timestamps down to the start of each period. No upload required.

Calculate Date Difference in JSON Files Online

Calculate the difference between two date or timestamp columns in JSON files directly in your browser. Output in days, months, years, hours, minutes, or seconds — no upload required.

Sort JSON Files Online

Sort JSON files by any column, ascending or descending, directly in your browser.

Format Timestamps in CSV Files Online

Reformat timestamp and date columns in CSV files directly in your browser. Convert between ISO 8601, Unix epoch, US date, and custom strftime patterns — no upload required.

Format Timestamps in Excel Files Online

Reformat timestamp and date columns in Excel files directly in your browser. Convert between ISO 8601, Unix epoch, US date, and custom strftime patterns — no upload required.

Format Timestamps in Parquet Files Online

Reformat timestamp and date columns in Parquet files directly in your browser. Convert between ISO 8601, Unix epoch, US date, and custom strftime patterns — no upload required.

JSON Viewer Online

View and inspect JSON files directly in your browser. Browse rows, check column names and data types — no upload required, your data stays on your device.

Convert JSON to Parquet Online

Convert JSON files to Parquet format directly in your browser. No upload required — your data never leaves your device.