HDF5 and NetCDF Viewer Online
Drop an HDF5 or NetCDF file to browse its groups and datasets, read every attribute, see the first values and plot a slice. No Python, no account and no upload.
NetCDF Viewer & HDF5 Viewer for VS Code and Cursor, free
- Maps with coastlines, a Play button that steps through time, and the time series of any map cell with one click.
- CF decoding with real dates, 8 color maps, Save PNG, and Export slice to CSV or JSON.
- Reads HDF5 compressed with LZF, Blosc, bitshuffle, Zstd, LZ4, bzip2 or ZFP, and files of many GB, slice by slice.
Optional Zovo Pro, USD 19 once: compare two files (like nccmp) and export a subset as NetCDF or CSV (like ncks -d). 3 free tries for each.
Drop an .h5 or .nc file here
or
HDF5 (.h5, .hdf5, .he5, .nxs), NetCDF-4 and NetCDF-3 (.nc), MATLAB 7.3 .mat, any size. Only the parts needed are read.
| Name | Type | Value |
|---|
First values
Open this in VS Code or Cursor
The free NetCDF Viewer & HDF5 Viewer extension opens .nc and .h5 files with a click inside VS Code and Cursor: maps with coastlines, a Play button that steps through time, the time series of any map cell, CF decoding with dates, 8 color maps and Save PNG. It reads files of many GB slice by slice, also over Remote SSH and WSL.
Free, MIT license. About NetCDF Viewer & HDF5 Viewer for VS Code.
Zovo Pro
Compare two files and export a subset. Zovo Pro, USD 19 once.
In the NetCDF Viewer & HDF5 Viewer extension, Zovo Pro compares two files like nccmp (shapes, attributes and every value after CF decoding, with the max difference and RMSE per variable) and exports a subset of a variable, by index or by coordinate value and date, as a NetCDF or CSV file. Each Pro tool works 3 times for free. One payment covers the Pro tools in 22 Zovo extensions. Everything that is free stays free.
After a card payment you get a key on the page. With GitHub Sponsors you sign in from the extension. Details on the Zovo Pro page.
Related tools
- NetCDF Viewer & HDF5 Viewer on the VS Code Marketplace (also on Open VSX). Browses NetCDF, HDF5 and MATLAB .mat files in VS Code.
- Parquet Viewer & Parquet Explorer. Opens large Parquet files with nested data in VS Code.
- NPZ, NPY, PyTorch and GGUF Viewer. Shows tensors, shapes, stats and heatmaps from model files in VS Code.
- TIFF Viewer & TIF Viewer. Opens TIFF and GeoTIFF images, 16-bit included, in VS Code.
- NPY and NPZ Viewer Online, free in your browser.
- TIFF Viewer Online, free in your browser.
- Parquet Viewer Online, free in your browser.
Questions
Is my file uploaded anywhere?
No. The page reads the file inside this tab. Its Content Security Policy sets connect-src to none, so the page cannot send your data anywhere. The HDF5 library (h5wasm, HDF5 compiled to WebAssembly) runs in a background worker of the page: it loads once from cdn.jsdelivr.net at a pinned version, its hash is checked before it runs, and it reads your file where it is. Your file is never sent there.
Which files does it open?
HDF5 files whatever their name (.h5, .hdf5, .he5, .nxs, .h5ad, .jld2 and others), NetCDF-4 files, which are HDF5 inside, and NetCDF-3 classic, 64-bit offset and CDF-5 files (.nc, .cdf). MATLAB 7.3 .mat files are HDF5 too and open here. The format is found from the first bytes. HDF4, MATLAB v5 .mat files and Zarr are not HDF5, and the page says so.
How big a file can it open?
There is no size limit of its own. The file is not copied into memory: HDF5 reads only the bytes it needs, so a big file opens about as fast as a small one. In our test a 2 GB file opened in under a second. For a big dataset the page reads the first values and up to 512 x 512 points for the heatmap.
What does it show for a dataset?
Its type, shape, dimension names, chunks, compression and every attribute, the first values as a table (up to 1,000 values, or 100 rows by 30 columns of a 2-D slice), and a line chart for 1-D data or a heatmap for 2-D and bigger. A slice box steps through the leading axes, such as time. Values packed with scale_factor and add_offset are decoded and _FillValue cells are marked, with a box to turn that off.
Which compression works?
Deflate (gzip), shuffle, fletcher32, n-bit and scale-offset, the filters built into HDF5. Datasets compressed with plugin filters (LZF, Blosc, bitshuffle, Zstd, LZ4, bzip2, ZFP) show their type, shape and attributes, and a note in place of the values. The NetCDF Viewer & HDF5 Viewer extension for VS Code reads all of them.
Is a hostile or broken file safe to open?
Names, attributes and values are written as plain text, never as HTML, and the page allows only its own scripts and the pinned library. External links in a file are listed but never followed. A file cut short says how many bytes are missing. The reader runs in a worker, and a read that takes long can be stopped with one button.
Does it work offline?
Yes. After the first visit the page keeps a copy of its own files and of the pinned HDF5 library, so it opens files with no connection.
What is free and what is Zovo Pro?
Everything on this page is free. In the NetCDF Viewer & HDF5 Viewer extension for VS Code, maps with coastlines, Play, time series, Save PNG and Export slice are free too. Comparing two files and exporting a subset are Zovo Pro, with 3 free tries each. One USD 19 payment covers the Pro tools in every Zovo extension.