Plot CSV, Excel & TXT Files Online

Open a CSV, Excel workbook, text log or JSON file and get a zoomable line chart in seconds, even with millions of rows. Free, no account, and your file never leaves your device.

Open a CSV, Excel, TXT, JSON or MATLAB file

Drop it here or choose a file to chart it. Millions of rows are fine.

No file to hand? Try a sample:

Tip: drop several files to compare them.

Your file never leaves your device. It is read and charted by your browser. Nothing is uploaded.

At a glance

Input formats: CSV, TSV, TXT and DAT (comma, semicolon, tab, pipe or space-aligned columns), Excel .xlsx and .xlsm, JSON and JSON Lines, MATLAB .mat (v4 to v7.3).
First chart: Drawn as soon as the file is read: a sorted date-time or number column becomes the x axis and the first numeric column is plotted against it.
Chart types: Line, step, bar, area and scatter charts and histograms, with a left and a right y axis and up to 8 series per chart. Several charts side by side share a cursor and zoom together.
Summaries: Totals, counts and averages by day, week, month, quarter or year, by product or region, per time window or value band, side by side or stacked. Sales files open as monthly bar charts.
Big files: A 2-million-row CSV opens in about 1 second, 10 million rows in about 3 seconds, and an Excel sheet at the 1,048,576-row maximum in under 3 seconds.
Zoom and detail: Drag to zoom and the full detail reloads instantly. Peaks and dips stay visible at every zoom level. Double-click to reset.
Statistics: Count, missing values, min, max, mean and standard deviation for every column; distinct and most frequent values for text columns.
Export: Any chart as a PNG image, and the rows you are looking at as a CSV file.
Processing: Runs in your browser. Files are never uploaded.
Price: Free. No account or sign-up.

How to plot a CSV or Excel file

Open your file. Drop a CSV, Excel, TXT, JSON or MATLAB .mat file onto the plotter, or click “Choose a file”. A workbook opens on its first sheet with data; switch sheets (or the tables of a .mat file) from the menu in the top bar.
Pick what to plot. The first chart appears straight away. Choose the x axis and add series from the toolbar, click a column header to plot that column alone or shift-click to add it, and move a series to the right axis to give it its own scale.
Zoom, read and export. Drag across the chart to zoom into any range at full detail and double-click to reset. Check each column’s statistics in the side panel, and download the chart as a PNG image.

What people use it for

Test-rig and data-logger exports

Long measurement logs as CSV, TXT or DAT, including comment lines at the top, units rows and space-aligned columns. Zoom from the whole run down to a single event.

Sales and finance exports from Excel

Plot revenue or units over time straight from an .xlsx file. Dates, percentages and the saved results of formulas come through as values, and report titles above the header are skipped.

Smart meter and IoT sensor logs

Half-hourly meter readings or sensor events as CSV or JSON Lines, on a real time axis, with clock changes and time zones handled.

Fitness and GPS exports

Heart rate, pace and elevation per second from a workout export, with elapsed times such as 01:02:03 as the x axis.

Checking a CSV before a database import

See which columns are numbers, dates or text, how many values are missing and whether the minimum and maximum make sense, before you load the file anywhere.

Comparing two runs

Overlaying two files on one chart is coming soon. Today you can plot several columns of one file together, on two y axes if their scales differ.

Supported file formats

The plotter recognises the format from the file’s content, so a CSV saved with a .txt name opens just as well. For .mat files, see the MAT file viewer page.

Format	Files	What works	Limits
Delimited text	.csv, .tsv, .txt, .dat	Comma, semicolon, tab, pipe or space-aligned columns. Finds the header, skips comment lines (#, //) and metadata above it, reads units rows, decimal commas and UTF-8, UTF-16 or Windows-1252 text.	Any size
Excel workbook	.xlsx, .xlsm	Every sheet, hidden ones included, from the sheet menu. Dates, times, percentages, booleans and the saved results of formulas. Finds the header below title rows.	Up to Excel’s 1,048,576 rows per sheet. Macros never run.
JSON	.json, .jsonl, .ndjson	Arrays of objects (nested fields become columns such as meta.sensor), arrays of rows, { "data": [...] } wrappers and JSON Lines.	JSON Lines and top-level arrays: any size. Other JSON up to 256 MB.
MATLAB	.mat	MATLAB v4, v6, v7 and v7.3 files. Finds your signals automatically: Simulink logs, dSPACE exports, structs, matrices with channel names and time vectors, each group in its own table.	Files of several GB. MATLAB table and datetime objects not yet.
Old Excel	.xls	Not supported. Open the file in Excel and save it as .xlsx.	A clear message tells you what to do.
Password-protected workbooks	.xlsx	Not supported. Remove the password in Excel first.
OpenDocument	.ods	Not yet. Save the file as .xlsx or CSV.
Engineering formats	TDMS, MF4	Coming later. Export to CSV for now.

Built for big files

Spreadsheets slow down long before a million rows, and Excel stops at 1,048,576. The plotter is made for files far bigger than that and opens them in seconds, right in your browser. In our tests in Chrome on a recent laptop:

a 143 MB CSV with 2,000,000 rows and 9 columns opened in about 1 second;
a 423 MB CSV with 10,000,000 rows and 5 columns opened in about 3 seconds;
an Excel workbook at the maximum of 1,048,576 rows (6 columns, 49 MB) opened in under 3 seconds;
a JSON Lines file with 100,000 events (12 MB) opened in about 0.3 seconds.

A one-sample spike in 10 million rows is still visible in the overview, and zooming in reloads the exact values of the visible range instantly. Slower machines take longer, and very large files need enough free memory.

Private by design: nothing is uploaded

Many online chart makers upload your file to a server first. MegaRows does not: the plotter runs entirely in your browser, on your device, and the file and its name are never sent anywhere. That makes it safe for test data, customer exports and financial figures that must stay on your computer. Read the privacy statement for details.

Frequently asked questions

How do I plot a CSV file?

Drop the file onto the plotter at the top of this page or click “Choose a file”. The first chart appears as soon as the file is read, with a time or number column on the x axis and the first numeric column as a line. Pick other columns from the toolbar or by clicking the column headers. There is nothing to install and the file is not uploaded.

How can I plot Excel data online without uploading it?

Open the .xlsx or .xlsm file here and your browser reads it on your own device. The plotter opens the first sheet with data and finds the header row, even below a report title; switch sheets from the menu in the top bar. Dates, times, percentages and the saved results of formulas are read as values. Old .xls files need to be saved as .xlsx in Excel first.

Can I plot more than 1 million rows?

Yes. Files far beyond Excel’s limit of 1,048,576 rows open in seconds: in our tests in Chrome, a 2-million-row CSV took about 1 second and a 10-million-row CSV about 3 seconds. Peaks and dips stay visible in the overview, and when you zoom in the full detail reloads instantly.

Can I plot two y axes (a dual y axis chart)?

Yes. Move any series to the right axis with the L / R button in the toolbar or from the column header menu, and it gets its own scale. That is how you show temperature and pressure, or units and revenue, on one chart. Up to eight series fit on the two axes.

Does my file get uploaded?

No. The file is read and charted by your browser on your own device, and neither the file nor its name is sent anywhere. You can check this in the Network tab of your browser’s developer tools while a file loads.

Can I calculate new channels, filters or spectra?

Yes. The Math button turns formulas (for example the magnitude of three axes), low-pass, high-pass and band-pass filters, moving averages and integrals into new channels you can plot like any column. It also opens FFT and PSD plots with a Grms readout, transfer functions with coherence, shock response spectra, rainflow cycle tables and statistics. Everything is calculated on your device, your math channels come back when you open the file again, and our results are checked against SciPy.

Which chart types are supported?

Line, step, bar, area and scatter charts, and histograms, all with drag-to-zoom, a crosshair with live values and PNG export. Any chart can also summarise its rows: sales by month, quarter or year, totals by product or region (side by side or stacked), the average of a signal every 10 seconds, or the time spent in each speed band. A file of sales or orders opens as a monthly bar chart, and the summary can be downloaded as a CSV. Box plots are coming soon.

Can I compare two files on one chart?

Yes. Choose or drop several files at once, or use “Add file”, and plot channels from each of them together: run A against run B, before and after a change, or this year’s sales against last year’s. Runs that started at different times can be lined up at their start, and the files can be compared side by side in tables with the differences worked out for you. Up to eight files can be open together, and your plots come back when you open the same files again.

Which file formats can I open?

CSV, TSV, TXT and DAT files with any common separator (comma, semicolon, tab, pipe or space-aligned columns), Excel workbooks (.xlsx and .xlsm), JSON or JSON Lines, and MATLAB .mat files from v4 to v7.3, including Simulink and dSPACE exports. The format is recognised from the file’s content, not only its name. TDMS and MF4 measurement files are planned for later.

Why won’t my .xls file open?

Files from Excel 97–2003 use an old binary format that MegaRows does not read. Open the file in Excel or LibreOffice, choose Save As → Excel Workbook (.xlsx), and open the new file here. Password-protected workbooks cannot be opened either, so remove the password in Excel first.

Coming soon to MegaRows: Sort, filter and search · CSV, Excel, JSON and PDF converters · Split and compare.

MegaRows processes files locally in your browser. Nothing is uploaded, not even the file name.