diff --git a/dist/hytale_plugin.js b/dist/hytale_plugin.js
index 10ed530..72d09aa 100644
--- a/dist/hytale_plugin.js
+++ b/dist/hytale_plugin.js
@@ -1871,6 +1871,116 @@
     }
   };
 
+  // src/uv_fill.ts
+  function setupUVFill() {
+    const fillModeSelect = BarItems.fill_mode;
+    fillModeSelect.options["uv"] = { name: "UV" };
+    const originalUseFilltool = Painter.useFilltool;
+    Painter.useFilltool = function(texture, ctx, x, y, area) {
+      if (fillModeSelect.get() !== "uv") {
+        return originalUseFilltool.call(Painter, texture, ctx, x, y, area);
+      }
+      uvRegionFill(texture, ctx, x, y, area);
+    };
+    track({
+      delete() {
+        Painter.useFilltool = originalUseFilltool;
+        delete fillModeSelect.options["uv"];
+      }
+    });
+  }
+  function uvRegionFill(texture, ctx, x, y, area) {
+    const region = findFaceRegion(texture, x, y, area.uvFactorX, area.uvFactorY);
+    if (!region) return;
+    const clickedAlpha = ctx.getImageData(Math.floor(x), Math.floor(y), 1, 1).data[3];
+    if (clickedAlpha === 0) {
+      fillTransparent(ctx, region);
+    } else if (isFlatColor(ctx, region)) {
+      fillRegion(ctx, region);
+    }
+  }
+  function findFaceRegion(texture, x, y, uvFactorX, uvFactorY) {
+    const animOffset = texture.display_height * texture.currentFrame;
+    for (const cube of Cube.all) {
+      for (const faceKey in cube.faces) {
+        const face = cube.faces[faceKey];
+        const faceTexture = face.getTexture();
+        if (!faceTexture || Painter.getTextureToEdit(faceTexture) !== texture) continue;
+        const uv = face.uv;
+        if (!uv) continue;
+        const minX = Math.floor(Math.min(uv[0], uv[2]) * uvFactorX);
+        const maxX = Math.ceil(Math.max(uv[0], uv[2]) * uvFactorX);
+        const minY = Math.floor(Math.min(uv[1], uv[3]) * uvFactorY) + animOffset;
+        const maxY = Math.ceil(Math.max(uv[1], uv[3]) * uvFactorY) + animOffset;
+        if (x >= minX && x < maxX && y >= minY && y < maxY) {
+          return { minX, minY, maxX, maxY };
+        }
+      }
+    }
+    for (const mesh of Mesh.all) {
+      for (const faceKey in mesh.faces) {
+        const face = mesh.faces[faceKey];
+        const faceTexture = face.getTexture();
+        if (!faceTexture || Painter.getTextureToEdit(faceTexture) !== texture) continue;
+        if (face.vertices.length < 3) continue;
+        let minX = Infinity, minY = Infinity, maxX = -Infinity, maxY = -Infinity;
+        for (const vkey in face.uv) {
+          const uv = face.uv[vkey];
+          minX = Math.min(minX, uv[0] * uvFactorX);
+          maxX = Math.max(maxX, uv[0] * uvFactorX);
+          minY = Math.min(minY, uv[1] * uvFactorY);
+          maxY = Math.max(maxY, uv[1] * uvFactorY);
+        }
+        minX = Math.floor(minX);
+        minY = Math.floor(minY) + animOffset;
+        maxX = Math.ceil(maxX);
+        maxY = Math.ceil(maxY) + animOffset;
+        if (x >= minX && x < maxX && y >= minY && y < maxY) {
+          return { minX, minY, maxX, maxY };
+        }
+      }
+    }
+    return null;
+  }
+  function isFlatColor(ctx, region) {
+    const width = region.maxX - region.minX;
+    const height = region.maxY - region.minY;
+    if (width <= 0 || height <= 0) return false;
+    const data = ctx.getImageData(region.minX, region.minY, width, height).data;
+    const [r, g, b, a] = [data[0], data[1], data[2], data[3]];
+    for (let i = 4; i < data.length; i += 4) {
+      if (data[i] !== r || data[i + 1] !== g || data[i + 2] !== b || data[i + 3] !== a) {
+        return false;
+      }
+    }
+    return true;
+  }
+  function fillRegion(ctx, region) {
+    const opacity = BarItems.slider_brush_opacity.get() / 255;
+    ctx.save();
+    ctx.fillStyle = tinycolor(ColorPanel.get()).setAlpha(opacity).toRgbString();
+    ctx.fillRect(region.minX, region.minY, region.maxX - region.minX, region.maxY - region.minY);
+    ctx.restore();
+  }
+  function fillTransparent(ctx, region) {
+    const width = region.maxX - region.minX;
+    const height = region.maxY - region.minY;
+    if (width <= 0 || height <= 0) return;
+    const imageData = ctx.getImageData(region.minX, region.minY, width, height);
+    const data = imageData.data;
+    const color = tinycolor(ColorPanel.get()).toRgb();
+    const alpha = Math.round(BarItems.slider_brush_opacity.get() / 255 * 255);
+    for (let i = 0; i < data.length; i += 4) {
+      if (data[i + 3] === 0) {
+        data[i] = color.r;
+        data[i + 1] = color.g;
+        data[i + 2] = color.b;
+        data[i + 3] = alpha;
+      }
+    }
+    ctx.putImageData(imageData, region.minX, region.minY);
+  }
+
   // src/plugin.ts
   BBPlugin.register("hytale_plugin", {
     title: "Hytale Models",
@@ -1895,6 +2005,7 @@
       setupPhotoshopTools();
       setupUVCycling();
       setupTextureHandling();
+      setupUVFill();
       let pivot_marker = new CustomPivotMarker();
       track(pivot_marker);
     },
diff --git a/src/plugin.ts b/src/plugin.ts
index 26a5c67..e692655 100644
--- a/src/plugin.ts
+++ b/src/plugin.ts
@@ -11,6 +11,7 @@ import { setupFormats } from "./formats";
 import { setupPhotoshopTools } from "./photoshop_copy_paste";
 import { CustomPivotMarker } from "./pivot_marker"
 import { setupTextureHandling } from "./texture";
+import { setupUVFill } from "./uv_fill";
 
 BBPlugin.register('hytale_plugin', {
     title: 'Hytale Models',
@@ -36,6 +37,7 @@ BBPlugin.register('hytale_plugin', {
         setupPhotoshopTools();
         setupUVCycling();
         setupTextureHandling();
+        setupUVFill();
 
         let pivot_marker = new CustomPivotMarker();
         track(pivot_marker)
diff --git a/src/uv_fill.ts b/src/uv_fill.ts
new file mode 100644
index 0000000..74ed25a
--- /dev/null
+++ b/src/uv_fill.ts
@@ -0,0 +1,153 @@
+import { track } from "./cleanup";
+
+interface UVRegion {
+	minX: number;
+	minY: number;
+	maxX: number;
+	maxY: number;
+}
+
+interface FillArea {
+	rect: number[];
+	uvFactorX: number;
+	uvFactorY: number;
+	w: number;
+	h: number;
+}
+
+// Adds "UV" fill mode: fills transparent areas or replaces flat-colored faces
+export function setupUVFill() {
+	const fillModeSelect = BarItems.fill_mode as BarSelect<string>;
+	fillModeSelect.options['uv'] = { name: 'UV' };
+
+	const originalUseFilltool = Painter.useFilltool;
+
+	Painter.useFilltool = function(texture: Texture, ctx: CanvasRenderingContext2D, x: number, y: number, area: FillArea) {
+		if (fillModeSelect.get() !== 'uv') {
+			return originalUseFilltool.call(Painter, texture, ctx, x, y, area);
+		}
+		uvRegionFill(texture, ctx, x, y, area);
+	};
+
+	track({
+		delete() {
+			Painter.useFilltool = originalUseFilltool;
+			delete fillModeSelect.options['uv'];
+		}
+	});
+}
+
+// Main fill logic: transparent click fills transparent pixels, flat color click replaces entire face
+function uvRegionFill(texture: Texture, ctx: CanvasRenderingContext2D, x: number, y: number, area: FillArea) {
+	const region = findFaceRegion(texture, x, y, area.uvFactorX, area.uvFactorY);
+	if (!region) return;
+
+	const clickedAlpha = ctx.getImageData(Math.floor(x), Math.floor(y), 1, 1).data[3];
+
+	if (clickedAlpha === 0) {
+		fillTransparent(ctx, region);
+	} else if (isFlatColor(ctx, region)) {
+		fillRegion(ctx, region);
+	}
+}
+
+// Returns UV bounds of the face containing the point, or null if none found
+function findFaceRegion(texture: Texture, x: number, y: number, uvFactorX: number, uvFactorY: number): UVRegion | null {
+	const animOffset = texture.display_height * texture.currentFrame;
+
+	for (const cube of Cube.all) {
+		for (const faceKey in cube.faces) {
+			const face = cube.faces[faceKey as CubeFaceDirection];
+			const faceTexture = face.getTexture();
+			if (!faceTexture || (Painter.getTextureToEdit(faceTexture) as Texture) !== texture) continue;
+
+			const uv = face.uv;
+			if (!uv) continue;
+
+			const minX = Math.floor(Math.min(uv[0], uv[2]) * uvFactorX);
+			const maxX = Math.ceil(Math.max(uv[0], uv[2]) * uvFactorX);
+			const minY = Math.floor(Math.min(uv[1], uv[3]) * uvFactorY) + animOffset;
+			const maxY = Math.ceil(Math.max(uv[1], uv[3]) * uvFactorY) + animOffset;
+
+			if (x >= minX && x < maxX && y >= minY && y < maxY) {
+				return { minX, minY, maxX, maxY };
+			}
+		}
+	}
+
+	for (const mesh of Mesh.all) {
+		for (const faceKey in mesh.faces) {
+			const face = mesh.faces[faceKey];
+			const faceTexture = face.getTexture();
+			if (!faceTexture || (Painter.getTextureToEdit(faceTexture) as Texture) !== texture) continue;
+			if (face.vertices.length < 3) continue;
+
+			let minX = Infinity, minY = Infinity, maxX = -Infinity, maxY = -Infinity;
+			for (const vkey in face.uv) {
+				const uv = face.uv[vkey];
+				minX = Math.min(minX, uv[0] * uvFactorX);
+				maxX = Math.max(maxX, uv[0] * uvFactorX);
+				minY = Math.min(minY, uv[1] * uvFactorY);
+				maxY = Math.max(maxY, uv[1] * uvFactorY);
+			}
+
+			minX = Math.floor(minX);
+			minY = Math.floor(minY) + animOffset;
+			maxX = Math.ceil(maxX);
+			maxY = Math.ceil(maxY) + animOffset;
+
+			if (x >= minX && x < maxX && y >= minY && y < maxY) {
+				return { minX, minY, maxX, maxY };
+			}
+		}
+	}
+
+	return null;
+}
+
+function isFlatColor(ctx: CanvasRenderingContext2D, region: UVRegion): boolean {
+	const width = region.maxX - region.minX;
+	const height = region.maxY - region.minY;
+	if (width <= 0 || height <= 0) return false;
+
+	const data = ctx.getImageData(region.minX, region.minY, width, height).data;
+	const [r, g, b, a] = [data[0], data[1], data[2], data[3]];
+
+	for (let i = 4; i < data.length; i += 4) {
+		if (data[i] !== r || data[i + 1] !== g || data[i + 2] !== b || data[i + 3] !== a) {
+			return false;
+		}
+	}
+	return true;
+}
+
+function fillRegion(ctx: CanvasRenderingContext2D, region: UVRegion) {
+	const opacity = (BarItems.slider_brush_opacity as BarSlider).get() / 255;
+
+	ctx.save();
+	ctx.fillStyle = tinycolor(ColorPanel.get()).setAlpha(opacity).toRgbString();
+	ctx.fillRect(region.minX, region.minY, region.maxX - region.minX, region.maxY - region.minY);
+	ctx.restore();
+}
+
+function fillTransparent(ctx: CanvasRenderingContext2D, region: UVRegion) {
+	const width = region.maxX - region.minX;
+	const height = region.maxY - region.minY;
+	if (width <= 0 || height <= 0) return;
+
+	const imageData = ctx.getImageData(region.minX, region.minY, width, height);
+	const data = imageData.data;
+	const color = tinycolor(ColorPanel.get()).toRgb();
+	const alpha = Math.round((BarItems.slider_brush_opacity as BarSlider).get() / 255 * 255);
+
+	for (let i = 0; i < data.length; i += 4) {
+		if (data[i + 3] === 0) {
+			data[i] = color.r;
+			data[i + 1] = color.g;
+			data[i + 2] = color.b;
+			data[i + 3] = alpha;
+		}
+	}
+
+	ctx.putImageData(imageData, region.minX, region.minY);
+}