Free Online GRO Viewer (No Signup)
Also opens DWG, DXF, STEP, IGES, IFC, SKP, STL, OBJ, GLB, FBX, 3DM and other 3D/CAD files. Drop any file on the viewer.
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Describe a compound, a protein or a crystal. The AI finds it in PubChem or the Protein Data Bank, or builds it, and opens it here.
Create a model with AI
Describe what you need, or add a photo, and AI builds it at real size in the viewer. Ask for changes in the chat, then export it. Free, with your own Anthropic or OpenAI key.
Open the AI GeneratorWhat Is a GRO File?
A .gro file is plain text. The first line is a title, the second the number of atoms, and each atom line gives the residue number and name, the atom name and number and the x, y and z position in nanometres, optionally followed by velocities. The last line is the box: three lengths for a rectangular box, nine numbers for a triclinic one.
GROMACS writes .gro files when it builds a system (gmx pdb2gmx, gmx solvate, gmx genion) and at the end of a run (confout.gro), and gmx trjconv writes frames of a trajectory as .gro. A system is usually a protein or a membrane surrounded by thousands of water molecules and ions.
For the Protein Data Bank format, see the PDB viewer; for every molecular format on one page, the molecule viewer.
Who Uses GRO Files?
Researchers and students running molecular dynamics with GROMACS, biophysicists simulating proteins and membranes, teachers of computational chemistry courses, and anyone who wants a quick look at a system on a laptop, tablet or phone away from the cluster.
Common Use Cases
- Check a solvated, ionised system before starting a run
- Look at the last frame of a simulation without copying it to a workstation with VMD
- See the simulation box around a protein or a membrane
- Share a snapshot with a supervisor or a colleague as a link that opens in any browser
- Export a frame as GLB or OBJ for a figure, a render or a slide
Features
Opens .gro Files
GROMACS structures and snapshots, converted from nanometres to ångströms.
The Simulation Box
A rectangular box drawn as the Unit cell layer.
Cartoon of Every Chain
Helices and strands as ribbons from the file, or worked out from the Cα trace; one chain coloured blue to red, several chains each in its own colour.
DNA and RNA
Nucleic acids as a tube along the backbone with the bases as sticks.
Ligands as Ball and Stick
Bound ligands, cofactors and ions drawn as ball and stick, coloured by element.
Water and Ions on Their Own Layers
Water starts on a switched-off layer so the protein or membrane is visible.
Export to GLB, STL or USDZ
Save the structure as GLB, glTF, OBJ, STL, 3MF, PLY, FBX or USDZ for a render, a 3D print or AR, or the view as a PNG.
Measure in Ångströms
Click two atoms to measure the distance between them, in Å.
View in VR
On a headset browser the molecule stands on a table in front of you.
Nothing Is Uploaded
The file is read entirely in your browser. No account, no upload, no copy on a server.
Share and Embed
Send a link that opens the molecule in any browser, or drop the viewer into your own page with one iframe.
Compatibility & Format Notes
Atom lines and the box line are read. Positions are converted from nanometres to ångströms, so the structure measures the same as its PDB file. The element of each atom is worked out from its atom and residue names, and bonds from covalent radii (a .gro file lists no bonds). A rectangular box is drawn as the Unit cell layer. Velocities are read past, and only the first frame of a file with several is drawn.
Proteins open as a cartoon: helices and strands as ribbons, taken from the file’s secondary-structure records when it has them and worked out from the Cα trace when it does not, with loops as a round tube. A single chain is coloured along its sequence from blue at the start to red at the end; when there are several chains, each gets its own colour. DNA and RNA open as a tube along the backbone with the bases as sticks. Ligands are drawn as ball and stick, coloured by element (carbon grey, oxygen red, nitrogen blue, sulfur yellow, in the Jmol colours).
Each representation is a layer you can switch on and off: Cartoon, Polymer atoms (every heavy atom of the chains as sticks), Hydrogens, Ligands, Water, Space filling (every atom except water as a sphere at its van der Waals radius) and Unit cell when the file gives one. Cartoon and ligands are on when the file opens; the rest wait in the Layers panel.
Coordinates are read in ångströms (Å) and kept at that scale, so the measuring tool reads distances in Å. Bonds are taken from the file where it lists them and worked out from covalent radii for the rest. Very large structures, such as a whole virus capsid with millions of atoms, open with the cartoon and with their atoms drawn as points so the browser keeps up.
Embed on Your Website
Add this viewer to your own site with a single line of HTML. Click Embed in the toolbar to generate an embed code, or use the snippet below with your own file URL.
Your Files Stay on Your Computer
Your GRO files are parsed entirely in your browser. Nothing is uploaded, stored, or shared unless you explicitly click the Share button. Shared files are hosted for 90 days then deleted.
Frequently Asked Questions
▶Why does my system open without its water?
The Water layer starts switched off so the protein or membrane is visible. Switch it on in the Layers panel to see the solvent.
▶What units are used?
GROMACS stores nanometres; the viewer converts them to ångströms, the unit of the other molecular formats, and the measuring tool reads Å.
▶Is the simulation box shown?
A rectangular box is, as the Unit cell layer drawn from the last line of the file. A triclinic box (nine numbers) is read past.
▶Can I play a trajectory?
No. The viewer draws one frame: the first one in the file. Use gmx trjconv -dump to write the frame you want as its own .gro file.
▶How are bonds worked out?
A .gro file holds no bonds, so they are inferred from the distance between atoms and their covalent radii.
▶Can I 3D print the molecule?
Yes. Export STL or 3MF and open it in your slicer. Thin cartoon ribbons and sticks are fragile at small sizes, so for a sturdy print switch on Space filling (or ball and stick for a small molecule) before exporting, and scale the model up in the slicer: one ångström in the file is one unit in the export.
▶Is this GRO viewer really free?
Yes, completely free. No signup, no watermarks, no file size limits on the viewer (the optional share-link feature has a 100 MB upload cap). Built by Innerscene as a tool for architects, engineers, and designers.
▶Are my files uploaded to a server?
No. All parsing, rendering, and conversion runs in your browser: nothing is uploaded, stored, or transmitted by default. The Share button is the only feature that uploads a file, and only when you explicitly click it.
▶Can I convert to another format?
Yes. Click Export in the toolbar to save the structure as GLB, glTF, OBJ, STL, 3MF, PLY, FBX or USDZ, or the view as a PNG picture. The export carries the layers you have switched on, so turn on Space filling or Polymer atoms first if you want them in the file. There is no PDB or SDF writer: the exports are 3D models of the picture you see.
▶Can I embed this viewer on my own site?
Yes. Click Embed in the toolbar to generate a one-line <iframe> snippet you can paste into any HTML page. You can choose whether the embed shows the viewer’s toolbar.