diff --git a/README.md b/README.md
new file mode 100644
index 0000000..ab195ab
--- /dev/null
+++ b/README.md
@@ -0,0 +1,25 @@
+# Scrap Tracer
+
+Turn a phone photo of a laser-cut scrap piece into a 1:1 DXF/SVG outline, so you can check in
+RDWorks (or LightBurn/Inkscape) whether your design fits on it. Built for Makerspace Delft.
+
+## Use
+
+1. Photograph the piece from straight above, on a contrasting surface, with something of known length visible.
+2. Load the photo, click **Measure**, click both ends of the known length, and enter it in mm.
+3. Check the green outline. If needed, adjust the threshold, tick "darker than background",
+   click the piece, or draw the outline by hand.
+4. Set the safety margin (default −2 mm shrinks the usable area a little).
+5. Download DXF and import it in your laser software at 1:1, in mm.
+
+## Develop
+
+    npm install
+    npm run dev      # local dev server
+    npm test         # unit tests (Vitest, OpenCV runs headless in Node)
+    npm run check    # type check
+    npm run build    # static build in dist/
+
+## Deploy (Cloudflare Pages)
+
+Build command `npm run build`, output directory `dist`. No server or environment variables needed.
diff --git a/src/App.svelte b/src/App.svelte
index da42345..18374ff 100644
--- a/src/App.svelte
+++ b/src/App.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import { onMount } from 'svelte';
   import ImageCanvas from './components/ImageCanvas.svelte';
+  import Sidebar from './components/Sidebar.svelte';
   import { AppState } from './lib/app-state.svelte';
   import { loadOpenCV } from './lib/opencv-loader';
 
@@ -22,10 +23,7 @@
 
 <div class="layout">
   <aside>
-    <input type="file" accept="image/*" onchange={(e) => {
-      const file = e.currentTarget.files?.[0];
-      if (file) app.loadFile(file);
-    }} />
+    <Sidebar {app} />
   </aside>
   <main ondragover={(e) => e.preventDefault()} {ondrop}>
     {#if app.image}
diff --git a/src/components/Sidebar.svelte b/src/components/Sidebar.svelte
new file mode 100644
index 0000000..d9bdcf4
--- /dev/null
+++ b/src/components/Sidebar.svelte
@@ -0,0 +1,112 @@
+<script lang="ts">
+  import type { AppState, Tool } from '../lib/app-state.svelte';
+  import { downloadText } from '../lib/download';
+  import { toDxf } from '../lib/export-dxf';
+  import { toSvg } from '../lib/export-svg';
+  import { scrapFilename, shapeSize } from '../lib/geometry';
+
+  let { app }: { app: AppState } = $props();
+
+  const size = $derived(app.exportShape ? shapeSize(app.exportShape) : null);
+  const nothingDetected = $derived(app.cv !== null && app.image !== null && app.shapePx === null);
+
+  function toggle(tool: Tool) {
+    app.tool = app.tool === tool ? 'none' : tool;
+  }
+
+  function onFile(e: Event & { currentTarget: HTMLInputElement }) {
+    const file = e.currentTarget.files?.[0];
+    if (file) app.loadFile(file);
+  }
+
+  function exportAs(ext: 'dxf' | 'svg') {
+    const shape = app.exportShape;
+    if (!shape) return;
+    const text = ext === 'dxf' ? toDxf(shape) : toSvg(shape);
+    downloadText(scrapFilename(shape, ext), text, ext === 'dxf' ? 'application/dxf' : 'image/svg+xml');
+  }
+</script>
+
+<h1>Scrap Tracer</h1>
+
+{#if app.cvError}
+  <p class="error">{app.cvError} <button onclick={() => location.reload()}>Reload</button></p>
+{:else if !app.cv}
+  <p class="muted">Loading image processing…</p>
+{/if}
+
+<section>
+  <h2>1. Photo</h2>
+  <label class="file">Load photo <input type="file" accept="image/*" onchange={onFile} /></label>
+  {#if app.loadError}<p class="error">{app.loadError}</p>{/if}
+</section>
+
+<section class:disabled={!app.image}>
+  <h2>2. Scale</h2>
+  <p class="muted">Click both ends of something whose length you know.</p>
+  <button class:active={app.tool === 'scale'} onclick={() => toggle('scale')} disabled={!app.image}>
+    {app.scalePoints.length === 2 ? 'Re-measure' : 'Measure'}
+  </button>
+  <label>Length <input type="number" min="1" step="any" bind:value={app.lengthMm} /> mm</label>
+  {#if app.scaleInvalid}
+    <p class="error">Enter a length above 0 and pick two different points.</p>
+  {:else if app.pxPerMm}
+    <p class="muted">{app.pxPerMm.toFixed(2)} px/mm</p>
+  {/if}
+</section>
+
+<section class:disabled={!app.image}>
+  <h2>3. Outline</h2>
+  {#if app.mode === 'auto'}
+    <label>Threshold <input type="range" min="0" max="255" bind:value={app.threshold} /> {app.threshold}</label>
+    <button onclick={() => app.autoThreshold()} disabled={!app.cv || !app.image}>Auto</button>
+    <label><input type="checkbox" bind:checked={app.invert} /> Piece is darker than background</label>
+    <button class:active={app.tool === 'seed'} onclick={() => toggle('seed')} disabled={!app.image}>Click to pick piece</button>
+  {/if}
+  <button class:active={app.tool === 'draw'} onclick={() => toggle('draw')} disabled={!app.image}>
+    {app.manualOuter.length === 0 ? 'Draw outline manually' : 'Draw a hole'}
+  </button>
+  {#if app.drawing.length > 0}
+    <button onclick={() => app.finishPolygon()}>Finish {app.manualOuter.length === 0 ? 'outline' : 'hole'}</button>
+  {/if}
+  {#if app.mode === 'manual' || app.drawing.length > 0}
+    <button onclick={() => app.clearManual()}>Back to automatic</button>
+  {/if}
+  {#if nothingDetected}
+    <p class="warning">Nothing detected, try adjusting the threshold or invert, or draw manually.</p>
+  {/if}
+</section>
+
+<section class:disabled={!app.pxPerMm}>
+  <h2>4. Safety margin</h2>
+  <label>
+    <input type="range" min="-10" max="5" step="0.5" bind:value={app.marginMm} disabled={!app.pxPerMm} />
+    {app.marginMm} mm
+  </label>
+  {#if !app.pxPerMm}<p class="muted">Set the scale first.</p>{/if}
+</section>
+
+<section>
+  <h2>5. Export</h2>
+  {#if size}<p>Piece: {Math.round(size.width)} × {Math.round(size.height)} mm</p>{/if}
+  <button class="primary" onclick={() => exportAs('dxf')} disabled={!app.exportShape}>Download DXF</button>
+  <button onclick={() => exportAs('svg')} disabled={!app.exportShape}>Download SVG</button>
+  {#if !app.exportShape}
+    <p class="muted">{app.pxPerMm ? 'No outline to export yet.' : 'Set the scale first.'}</p>
+  {/if}
+</section>
+
+<style>
+  h1 { font-size: 1.3rem; margin: 0 0 12px; }
+  h2 { font-size: 1rem; margin: 0 0 6px; }
+  section { padding: 12px 0; border-top: 1px solid #eee; display: flex; flex-direction: column; gap: 6px; align-items: flex-start; }
+  section.disabled { opacity: 0.5; }
+  label { display: flex; gap: 6px; align-items: center; }
+  input[type='number'] { width: 80px; }
+  .file input { max-width: 200px; }
+  button.active { outline: 2px solid #2962ff; }
+  button.primary { font-weight: bold; }
+  .muted { color: #777; margin: 0; font-size: 0.9rem; }
+  .error { color: #c62828; margin: 0; }
+  .warning { color: #e65100; margin: 0; }
+</style>