SmartQueryTools

Sample NDJSON Files Online

Sample rows from NDJSON files — first N, last N, or random — directly in your browser.

How to sample NDJSON files

  1. Drop your file onto the upload area. It is loaded into the in-browser engine and the first 200 rows are shown.
  2. Pick a Method: First takes rows from the top, Last takes rows from the bottom, and Random picks rows from anywhere in the file.
  3. Enter the Number of rows you want. The default is 100.
  4. Click Sample. The preview shows the sampled rows and how many were taken.
  5. Click Download to save the sample 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 facilities team logs a cold-room temperature every two hours and only needs the latest three readings to check a door alarm.

Input (NDJSON)

{"reading_at":"2026-08-01 00:00:00","sensor":"cold-room-2","temp_c":3.8}
{"reading_at":"2026-08-01 02:00:00","sensor":"cold-room-2","temp_c":3.9}
{"reading_at":"2026-08-01 04:00:00","sensor":"cold-room-2","temp_c":4.1}
{"reading_at":"2026-08-01 06:00:00","sensor":"cold-room-2","temp_c":6.7}
{"reading_at":"2026-08-01 08:00:00","sensor":"cold-room-2","temp_c":7.2}
{"reading_at":"2026-08-01 10:00:00","sensor":"cold-room-2","temp_c":4}

Settings

  • Method: Last
  • Number of rows: 3

Result

reading_atsensortemp_c
2026-08-01 06:00:00cold-room-26.7
2026-08-01 08:00:00cold-room-27.2
2026-08-01 10:00:00cold-room-24

Last takes rows by their position in the file, not by the timestamp value. The file has six rows, so asking for three returns rows 4 to 6 in their original order. If the log were not already in time order, sort by reading_at first. Random with the same settings would return three rows from anywhere in the file.

Frequently Asked Questions

What happens if I ask for more rows than the file has?

You get every row. First and Last return the whole file, and Random returns all rows as well.

Is the random sample the same each time?

No. Every click of Sample draws a new random set, and the rows may not keep their file order. For a repeatable sample, use the SQL Query tool with USING SAMPLE reservoir(N ROWS) REPEATABLE (seed).

What is the difference between Sample and Head or Tail?

First and Last in this tool do the same as Head and Tail. Sample adds the Random method, which spreads the selection across the whole file.

Related Tools

Validate CSV Files Online

Validate CSV file structure in your browser. Check null counts, distinct values, and data types for every column — no upload required.

Count Values in CSV Files Online

Group and count rows by any column in CSV files directly in your browser. Sort by frequency or value to find the most common entries — no upload required.

Sort CSV Files Online

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

Sample CSV Files Online

Sample rows from CSV files — first N, last N, or random — directly in your browser.

Sample Excel Files Online

Sample rows from Excel files — first N, last N, or random — directly in your browser.

Sample Parquet Files Online

Sample rows from Parquet files — first N, last N, or random — directly in your browser.

Sample JSON Files Online

Sample rows from JSON files — first N, last N, or random — directly in your browser.

NDJSON Viewer Online

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