diff --git a/src/composables/usePngExport.ts b/src/composables/usePngExport.ts
index 305b2ac..c6adf14 100644
--- a/src/composables/usePngExport.ts
+++ b/src/composables/usePngExport.ts
@@ -2,14 +2,18 @@ import { ref } from 'vue'
 
 type Toast = { kind: 'ok' | 'err'; text: string } | null
 
-/** Slugified, stable download name derived from the plan title. */
-export function exportFilename(title: string): string {
-  const slug = title
+/** Lowercase, dash-collapsed slug of a plan title — no extension, no fallback. */
+export function slugify(title: string): string {
+  return title
     .toLowerCase()
     .trim()
     .replace(/[^a-z0-9]+/g, '-')
     .replace(/^-+|-+$/g, '')
-  return `macroplan-${slug || 'plan'}.png`
+}
+
+/** Slugified, stable download name derived from the plan title. */
+export function exportFilename(title: string): string {
+  return `macroplan-${slugify(title) || 'plan'}.png`
 }
 
 /**
diff --git a/src/composables/useSourceExport.test.ts b/src/composables/useSourceExport.test.ts
new file mode 100644
index 0000000..5e9ba32
--- /dev/null
+++ b/src/composables/useSourceExport.test.ts
@@ -0,0 +1,13 @@
+import { describe, it, expect } from 'vitest'
+import { sourceFilename } from './useSourceExport'
+
+describe('sourceFilename', () => {
+  it('slugifies the plan title into a .toml name', () => {
+    expect(sourceFilename('Q3 — Checkout revamp')).toBe('macroplan-q3-checkout-revamp.toml')
+  })
+
+  it('falls back to a generic name when the title has no usable characters', () => {
+    expect(sourceFilename('')).toBe('macroplan-plan.toml')
+    expect(sourceFilename('—— ··')).toBe('macroplan-plan.toml')
+  })
+})
diff --git a/src/composables/useSourceExport.ts b/src/composables/useSourceExport.ts
new file mode 100644
index 0000000..328832e
--- /dev/null
+++ b/src/composables/useSourceExport.ts
@@ -0,0 +1,17 @@
+import { slugify } from './usePngExport'
+
+/** Slugified, stable download name for a plan's TOML source. */
+export function sourceFilename(title: string): string {
+  return `macroplan-${slugify(title) || 'plan'}.toml`
+}
+
+/** Download a plan's TOML source as a .toml file (client-side, no backend). */
+export function downloadSource(source: string, filename: string): void {
+  const blob = new Blob([source], { type: 'text/plain;charset=utf-8' })
+  const url = URL.createObjectURL(blob)
+  const a = document.createElement('a')
+  a.href = url
+  a.download = filename
+  a.click()
+  URL.revokeObjectURL(url)
+}