Free NIfTI Viewer
Open NIfTI volumes (.nii / .nii.gz) and DICOM slices right in your browser — no install, no account, no upload. Scroll axial, coronal and sagittal planes, read voxel intensity, window brightness, then switch to an interactive 3D volume render. Built for neuroimaging files from FreeSurfer, dcm2niix and research pipelines, and for hospital CDs you just want to look at privately.
- 🔒 100% private — no uploads
- 🆓 Free, no watermark
- 📱 Works on any device
How to open a NIfTI or DICOM scan
- 1
Open a NIfTI or DICOM file
Drop a .nii or .nii.gz volume, a single .dcm file, or a whole folder of DICOM slices. Compressed NIfTI is unzipped automatically; everything is read in your browser — never uploaded.
- 2
Browse the slices in 2D
Scroll with the mouse wheel and switch between axial, coronal and sagittal planes — or show all three at once. Click-drag to window brightness and contrast; click a voxel to read its intensity.
- 3
Switch to 3D
Open the interactive volume render, rotate and zoom with the mouse, and pick a colormap to highlight the structures you care about. Download a PNG of the current view when you need a screenshot.
Why use Free NIfTI Viewer?
NIfTI-first, private by design
Open the .nii / .nii.gz volumes used in neuroimaging and research without installing FSLeyes, MRIcroGL or 3D Slicer. Decoding and WebGL rendering stay on your device — ideal for patient data and lab volumes you do not want on a cloud uploader.
DICOM folders work too
Hospital CDs and USBs often ship as a folder of .dcm slices (sometimes with no file extension). Drop the folder; slices are assembled into a 3D volume on your machine via an in-browser dcm2niix conversion.
2D planes and a 3D volume render
Multiplanar axial / coronal / sagittal views, intensity windowing, live crosshair readout, then flip to a rotatable 3D render with selectable colormaps — no plugin, no account, no watermark.
Runs in any modern browser
Needs WebGL2 (current Chrome, Edge, Firefox or Safari). Works on Windows, macOS, Linux, and many phones and tablets — nothing to install.
What is a NIfTI file?
NIfTI (.nii and the gzip-compressed .nii.gz) is the standard volume format in neuroimaging and much of medical-image research. Tools like FreeSurfer, FSL, AFNI, dcm2niix and many deep-learning pipelines export brain and body scans as a single 3D (or 4D) file instead of thousands of DICOM slices. If someone sent you a .nii.gz from a study, lab, or open dataset, this page is a free online NIfTI viewer that opens it without installing desktop software.
Open .nii and .nii.gz without uploading
Most “online NIfTI viewers” ask you to upload the volume to their servers first. LocalTools decodes and renders the file with WebGL entirely on your device, so patient scans, unpublished research volumes and hospital data never leave your machine. Drop the file (or a whole DICOM folder), wait a moment for larger .nii.gz volumes, and explore the slices immediately.
NIfTI vs DICOM — which do I have?
DICOM (.dcm) is what scanners and PACS systems produce: often one file per slice, sometimes with no extension on a hospital CD. NIfTI is usually a single .nii or .nii.gz volume used after conversion (for example with dcm2niix) for analysis and ML. This viewer accepts both — NIfTI natively, and DICOM by converting the series to a volume on-device — so you do not need two apps to peek at either format.
2D multiplanar views and a 3D volume render
Scroll slices with the mouse wheel, switch among axial, coronal and sagittal (or show all three at once), and click-drag to window brightness and contrast. Click a point for a live voxel index and intensity readout. Then switch to 3D for a rotatable volume rendering with colormaps useful for soft tissue, bone-like contrast or overview screenshots. Download a PNG of the current view when you need to share a non-diagnostic snapshot.
Frequently asked questions
What is a NIfTI (.nii / .nii.gz) file?
NIfTI is a scientific medical-image format that stores a 3D (or 4D) volume in one file. .nii is uncompressed; .nii.gz is the same data gzip-compressed and is what most research pipelines produce. This viewer opens both in the browser.
How do I open a .nii.gz without installing software?
Drop the .nii.gz onto this page (or click to browse). The file is decompressed and rendered locally with WebGL — no FSLeyes, MRIcroGL, 3D Slicer or MATLAB install required. Large files may take a few seconds on first open.
What file formats can I open?
NIfTI (.nii and .nii.gz) and DICOM (.dcm). For DICOM you can drop a single file or a whole folder of slices — including extensionless files from many hospital CDs — and they are assembled into a 3D volume on your device.
NIfTI vs DICOM — what is the difference?
DICOM is the clinical exchange format from scanners (often many slice files). NIfTI is the research-friendly single-volume format used after conversion. Use this viewer for either: open .nii/.nii.gz directly, or drop a DICOM folder to convert and view it locally.
Are my scans uploaded to a server?
No. The viewer reads, decodes and renders your NIfTI or DICOM file entirely in your browser. Your files never leave your device, so it even works offline once the page has loaded — ideal for confidential medical and research images.
Can I view a brain MRI or research fMRI NIfTI?
Yes for structural 3D NIfTI volumes (typical brain MRI, CT-derived .nii.gz, atlas volumes, and most research exports). Time-series / 4D fMRI can open as a volume, but this tool is built for spatial browsing and 3D rendering — not full 4D time scrubbing or analysis.
Why won’t my hospital CD open?
Many CDs store DICOM slices without a .dcm extension, or nest them in folders. Drop the whole folder (not only one file). The viewer sniffs the DICOM “DICM” magic bytes so extensionless slices still load. Multi-series studies currently load the first series found.
Can I use this for diagnosis?
No. This is a general-purpose NIfTI and DICOM viewer for looking at and sharing scans — it is not a certified medical device and is not for diagnostic use. Always rely on your radiologist and approved clinical software for any medical decision.
Does it cost anything or add a watermark?
No. The NIfTI and DICOM viewer is free, has no file-size paywall and never adds a watermark. It only needs a modern browser with WebGL2.