Stroke Forge
Free online sprite outliner. Drop a transparent PNG, pick a color and width, get an outlined sprite.
Reads the alpha channel of a transparent PNG, dilates it outward by your chosen width, fills the ring with your stroke color, and composites the original on top. Add glow by dialing the blur slider. Drop opacity for a translucent halo. Output is a transparent PNG with the outline baked in.
Sprites, UI icons, and characters need outlines to read at any scale. Every game project ends up wanting one. Stroke Forge skips the trip to GIMP / Photoshop and the four-step layer-style ritual. Drop, dial, download.
- 01Drop a transparent PNG. Sprites and UI icons work best. Photo backgrounds with no alpha will not outline cleanly. Pair with BG Forge first if the source has a solid background.
- 02Dial Width to thicken the outline. The preview updates as you drag.
- 03Pick Color from the swatches or the color square. Black for line art, white for cel-shaded sprites, accent colors for UI selection states.
- 04Add Glow / Blur for a soft halo. Drop Opacity for a translucent outline.
- 05Download PNG. Copy PNG drops the result on your clipboard.
- Source needs alpha. JPGs and PNGs with a solid background have no transparent edge to dilate. Run BG Forge first.
- Width over ~20 px on small sprites swallows the original. Use the preview to dial in.
- Nothing leaves your machine. All compositing runs on the canvas in your tab.
Is Stroke Forge free, and does it add a watermark?
Yes, completely free. No account, no upload, no watermark on the output.
How do I add an outline to a transparent PNG online?
Drop your PNG, dial the Width slider to set thickness, pick a color, and Download. The tool dilates the image's alpha channel outward, fills the ring with your stroke color, and composites the original on top — same technique Photoshop's Stroke layer-style uses, just one slider instead of four.
Will it work on a JPG or a photo with a solid background?
No. Stroke Forge reads the alpha channel, and JPGs / solid-background images don't have one. Run BG Forge first to get a transparent cut-out, then send it to Stroke Forge.
Can I add a glow or halo effect?
Yes. The Glow / Blur slider softens the outline into a halo. Drop Opacity for a translucent version. Combine width + glow + low opacity for the classic 'selected sprite' UI look.
What outline thickness should I use?
1-3 px for crisp pixel-art sprites. 4-8 px for cel-shaded characters and UI icons. Anything over ~20 px on small sprites starts swallowing the original — use the live preview to dial it in.
What format is the export?
Transparent PNG with the outline baked in. Use Download PNG for a file, or Copy PNG to drop the result straight onto your clipboard.
Can I use the outlined sprites in commercial games?
Yes. Stroke Forge adds no watermark and asserts no rights over your output. Whatever rights you have to the source sprite carry through.
Where does my sprite go?
Nowhere. All compositing runs on the canvas in your browser tab. No upload, no server, no account.
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Start free14 days free, no card. Founding price $12 a month after that.