Overlay a rule-of-thirds grid on uploaded images to analyze and improve composition.
Composition guidance usually says to place the subject on a third, but picturing a two-line grid over a photograph is harder than it sounds. This tool makes the advice literal: load an image and it draws two vertical and two horizontal lines dividing the frame into three equal bands, with the four intersections marked. The frequent surprise is that it renders no verdict - the grid shows where the thirds fall, and judgment stays with you. The file never leaves your browser, and the lines derive from the image's own pixel dimensions, so the overlay scales correctly for any size or orientation.
A concrete input and expected output from the current implementation.
Input
A 3000 x 2000 px landscape photograph with the horizon running through the lower third of the frame.
Expected output
The image renders with the grid overlaid: vertical lines at 1000 px and 2000 px from the left edge, horizontal lines at 666.7 px and 1333.3 px from the top. Because the horizon sits in the lower third, it falls below the second horizontal line (1333.3 px), letting you judge whether it aligns with that line or sits between it and the bottom edge.
The grid divides the image's own dimensions into equal thirds: vertical lines at 3000/3 = 1000 px and two-thirds (2000 px); horizontal lines at 2000/3 = 666.7 px and two-thirds (1333.3 px). The image itself is unchanged.
The grid splits the uploaded image's own pixel width and height into three equal bands, placing a line at one-third and at two-thirds of each dimension and marking the four crossings. Because the divisions are computed from the image file rather than from a fixed screen template, the overlay is geometrically identical in proportion for any image: portrait, landscape, or square, 800 px wide or 8000.
The file you choose is read into the page and the grid is drawn over the loaded copy, so the check happens on your device and nothing is sent to a server. That is why the overlay appears as soon as the image loads and why the tool works with no network at all - which also makes it safe to use on images you would not want to share.
No. It overlays the grid and leaves the judgment to you. The rule of thirds is a long-standing convention about where the eye tends to land, not a measure of quality, and many strong images ignore it deliberately. Use the overlay to test placements, then decide for yourself.
No. The image is loaded and handled entirely within your browser and never leaves your device, so the tool works offline and your photos are not stored, transmitted, or available to anyone else. The trade-off is that the tool cannot compare images or offer learned suggestions - it sees only the single file you loaded.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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