diff --git a/index.html b/index.html
index 749b4c0..bb774e2 100644
--- a/index.html
+++ b/index.html
@@ -56,7 +56,7 @@
       .editor_container:focus-within, 
       .bottom:focus-within,
       .files_container:focus-within,
-      .help_dialog {
+      dialog {
         outline: none;
         box-shadow: 1px 1px 6px 3px var(--shadow_color);
       }
@@ -314,13 +314,8 @@
 
       /* status */
 
-      /*
-      .request_fullscreen {
-        margin-left: auto;
-      }
-      */
-
       .statusbar {
+        margin-bottom: 0px;
         grid-area: statusbar;
         display: flex;
         flex-direction: row;
@@ -384,8 +379,41 @@
         margin: 0em 0.5em;
       }
 
-      .help_dialog[open] {
+      .share_button, .upload_button {
         border: none;
+        color: white;
+        background: rgb(23 166 236);
+      }
+
+      .share_button {
+        font-size: 1.2em;
+        margin-left: 1em;
+        margin-right: 0.5em;
+      }
+      
+      .share_button[disabled] {
+        background: grey;
+      }
+
+
+      .share_dialog input, .share_dialog button {
+        font-size: 1.2em;
+      }
+
+      .share_dialog button {
+        padding: 5px;
+        height: 2em;
+      }
+
+      dialog {
+        border: none;
+      }
+
+      dialog::backdrop {
+        background-color: rgb(225 244 253 / 80%);
+      }
+
+      .help_dialog[open] {
         display: flex;
         flex-direction: column;
         justify-content: center;
@@ -396,10 +424,6 @@
         background-color: white;
       }
 
-      .help_dialog::backdrop {
-        background-color: rgb(225 244 253 / 80%);
-      }
-
       .help {
         padding: 2em;
         border-spacing: 5px;
diff --git a/src/cmd.js b/src/cmd.js
index 0eb304a..e7ade81 100644
--- a/src/cmd.js
+++ b/src/cmd.js
@@ -248,12 +248,13 @@ const input = (state, code, index) => {
     set_cursor_position({...state, files}, index),
     [state.current_module]
   )
-  const effect_save = next.current_module == ''
-    ? {type: 'save_to_localstorage', args: ['code', code]}
-    : {type: 'write', args: [
+  const effect_save = {
+    type: 'write', 
+    args: [
       next.current_module,
       next.files[next.current_module],
-    ]}
+    ]
+  }
   return {state: next, effects: [effect_save]}
 }
 
diff --git a/src/editor/share_dialog.js b/src/editor/share_dialog.js
new file mode 100644
index 0000000..12cc6b4
--- /dev/null
+++ b/src/editor/share_dialog.js
@@ -0,0 +1,92 @@
+import {el} from './domutils.js'
+import {save_share} from '../share.js'
+import {get_state} from '../index.js'
+
+export class ShareDialog {
+  constructor() {
+    this.el = el('dialog', 'share_dialog', 
+      this.upload_begin = el('p', '',
+        el('p', '',
+          'This button will upload your scratch file to the cloud for sharing with others.'),
+        el('ul', '', 
+          el('li', '', 
+            'Please ensure that no personal data or confidential information is included.'
+          ),
+          el('li', '', 
+            'Avoid including copyrighted materials.'
+          ),
+        ),
+        el('span', {style: 'color: red'}, 
+          'Caution: Once shared, files cannot be deleted.'
+        ),
+        this.upload_buttons = el('p', {style: 'text-align: center'}, 
+          el('button', {
+            'class': 'upload_button',
+            click: () => this.upload()
+          },
+            "Upload"
+          ),
+          this.cancel_button = el('button', {
+            style: 'margin-left: 1em',
+            click: () => this.cancel()
+          },
+            "Cancel"
+          )
+        ),
+      ),
+      this.uploading = el('span', {style: 'display: none'},
+        "Uploading..."
+      ),
+      this.upload_finish = el('p', {style: 'display: none'}, 
+        el('p', '', 
+          el('p', {style: `
+            text-align: center; 
+            margin-bottom: 1em; 
+            font-size: 1.2em
+          `}, 'Upload successful'),
+          this.url_share = el('input', {
+            type: 'text',
+            readonly: true,
+            style: 'min-width: 30em',
+          }),
+          this.copy_button = el('button', {
+            click: () => this.copy(),
+            style: 'margin-left: 1em',
+          }, 'Copy URL')
+        ),
+        this.close_button = el('button', {
+          style: 'display: block; margin: auto',
+          click: () => this.cancel(),
+        }, 'Close'),
+      )
+    )
+  }
+
+  async upload() {
+    this.uploading.style.display = ''
+    this.upload_begin.style.display = 'none'
+    try {
+      const id = await save_share(get_state().files[''])
+      this.url = new URL(window.location)
+      this.url.searchParams.append('share_id', id)
+      this.url_share.value = this.url
+      this.upload_finish.style.display = ''
+    } catch(e) {
+      alert(e.message)
+      this.upload_begin.style.display = ''
+    } finally {
+      this.uploading.style.display = 'none'
+    }
+  }
+
+  copy() {
+    this.url_share.select()
+    document.execCommand('copy')
+  }
+
+  cancel() {
+    this.upload_finish.style.display = 'none'
+    this.upload_begin.style.display = ''
+    this.el.close()
+  }
+}
diff --git a/src/editor/ui.js b/src/editor/ui.js
index 692b071..ec2687a 100644
--- a/src/editor/ui.js
+++ b/src/editor/ui.js
@@ -4,6 +4,7 @@ import {Files} from './files.js'
 import {CallTree} from './calltree.js'
 import {Logs} from './logs.js'
 import {IO_Trace} from './io_trace.js'
+import {ShareDialog} from './share_dialog.js'
 import {el} from './domutils.js'
 
 export class UI {
@@ -129,7 +130,12 @@ export class UI {
               href: 'https://github.com/leporello-js/leporello-js',
               target: '__blank',
             }, 'Github'),
+          el('button', {
+              'class': 'share_button',
+              'click': () => this.share_dialog.showModal(),
+            }, 'Share'),
           this.help_dialog = this.render_help(),
+          this.share_dialog = new ShareDialog().el,
         )
       ))
     )
diff --git a/src/effects.js b/src/effects.js
index 48eb077..623d3c0 100644
--- a/src/effects.js
+++ b/src/effects.js
@@ -299,8 +299,32 @@ export const EFFECTS = {
     localStorage[key] = value
   },
 
-  write: (state, [name, contents], ui) => {
-    if(state.has_file_system_access) {
+  write: (state, [name, contents], ui, prev_state) => {
+    if(name == '') {
+      const share_id = new URL(window.location).searchParams.get('share_id')
+      if(share_id == null) {
+        localStorage['code'] = contents
+      } else {
+        const key = 'share_' + share_id
+        if(localStorage['code'] == prev_state.files['']) {
+          /*
+            If scratch code is the same with share code, then update both
+
+            Imagine the following scenario:
+
+            - User shares code. URL is replaced with ?share_id=XXX
+            - He keeps working on code
+            - He closes browser tab and on the next day he opens app.leporello.tech
+            - His work is lost (actually, he can still access it with
+              ?share_id=XXX, but that not obvious
+
+            To prevent that, we keep updating scratch code after sharing
+          */
+          localStorage['code'] = contents
+        }
+        localStorage[key] = contents
+      }
+    } else if(state.has_file_system_access) {
       write_file(name, contents)
     } else {
       write_example(name, contents)
diff --git a/src/index.js b/src/index.js
index a227209..39fcec2 100644
--- a/src/index.js
+++ b/src/index.js
@@ -6,6 +6,7 @@ import {
   init_window_service_worker
 } from './filesystem.js'
 import {examples, examples_dir_promise} from './examples.js'
+import {get_share} from './share.js'
 
 const EXAMPLE = `function fib(n) {
   if(n == 0 || n == 1) {
@@ -178,41 +179,51 @@ export const init = async (container, _COMMANDS) => {
 
   set_error_handler(window)
 
-  const default_module = {'': localStorage.code || EXAMPLE}
+  let files = {'': localStorage.code || EXAMPLE}
   let initial_state, entrypoint_settings
   const project_dir = await open_dir(false)
   let example
   if(project_dir == null) {
     /*
-      extract example from URL params and delete it
+      extract example_id from URL params and delete it (because we dont want to
+      persist in on refresh)
     */
     const params = new URLSearchParams(window.location.search)
     const example_path = params.get('example')
-    params.delete('example')
-    globalThis.history.replaceState(
-      null, 
-      null, 
-      '/' + params.toString() + window.location.hash
-    )
+    const nextURL = new URL(window.location)
+    nextURL.searchParams.delete('example')
+    history.replaceState(null, null, nextURL.href)
 
     example = examples.find(e => e.path == example_path)
-    entrypoint_settings = example == null
-      ? get_entrypoint_settings()
-      : {
+
+    if(example == null) {
+      const shared_code = await get_share()
+      if(shared_code == null) {
+        entrypoint_settings = get_entrypoint_settings()
+      } else {
+        files = {'': shared_code}
+        entrypoint_settings = {
+          current_module: '',
+          entrypoint: '',
+        }
+      }
+    } else {
+      entrypoint_settings = {
         current_module: example.entrypoint,
         entrypoint: example.entrypoint,
       }
+    }
 
     initial_state = {
       project_dir: await examples_dir_promise,
-      files: default_module,
+      files,
       has_file_system_access: false,
     }
   } else {
     entrypoint_settings = get_entrypoint_settings()
     initial_state = {
       project_dir,
-      files: default_module,
+      files,
       has_file_system_access: true,
     }
   }
@@ -306,7 +317,7 @@ export const exec = (cmd, ...args) => {
         } else {
           console.log('apply effect', e.type, ...(e.args ?? []))
         }
-        EFFECTS[e.type](nextstate, e.args, ui)
+        EFFECTS[e.type](nextstate, e.args, ui, state)
       })
     }
   }, nextstate)
diff --git a/src/share.js b/src/share.js
new file mode 100644
index 0000000..4078d65
--- /dev/null
+++ b/src/share.js
@@ -0,0 +1,74 @@
+const PROJECT_ID = 'leporello-js'
+const URL_BASE = `https://firebasestorage.googleapis.com/v0/b/${PROJECT_ID}.appspot.com/o/`
+
+// see https://stackoverflow.com/a/48161723/795038
+async function sha256(message) {
+    // encode as UTF-8
+    const msgBuffer = new TextEncoder().encode(message);                    
+
+    // hash the message
+    const hashBuffer = await crypto.subtle.digest('SHA-256', msgBuffer);
+
+    // convert ArrayBuffer to Array
+    const hashArray = Array.from(new Uint8Array(hashBuffer));
+
+    // convert bytes to hex string                  
+    const hashHex = hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
+    return hashHex;
+}
+
+async function upload_share(text) {
+  const id = (await sha256(text))
+    // Truncate to 20 bytes, like in git
+    .slice(0, 40)
+  const blob = new Blob([text], { type: 'text/plain' })
+  const formData = new FormData()
+  formData.append('file', blob)
+  const response = await fetch(URL_BASE + id, {
+    method: 'POST',
+    body: formData
+  })
+  if(!response.ok) {
+    const json = await response.json()
+    const message = json?.error?.message
+    throw new Error('Failed to upload: ' + message)
+  }
+  return id
+}
+
+async function download_share(id) {
+  const response = await fetch(URL_BASE + id + '?alt=media')
+  if(!response.ok) {
+    const json = await response.json()
+    const message = json?.error?.message
+    throw new Error('Failed to fetch: ' + message)
+  }
+  return response.text()
+}
+
+export async function get_share() {
+  const params = new URLSearchParams(window.location.search)
+  const share_id = params.get('share_id')
+  if(share_id == null) {
+    return null
+  }
+
+  const shared_code = localStorage['share_' + share_id]
+  if(shared_code != null) {
+    return shared_code
+  }
+
+  try {
+    return await download_share(share_id)
+  } catch(e) {
+    alert(e.message)
+    return null
+  }
+}
+
+export async function save_share(text) {
+  const share_id = await upload_share(text)
+  const nextURL = new URL(window.location)
+  nextURL.searchParams.set('share_id', share_id)
+  history.replaceState(null, null, nextURL.href)
+}