diff --git a/src/main.rs b/src/main.rs
index 5eb24f5..36c4b24 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,7 +8,7 @@ use std::{fmt::Debug, path::PathBuf, str::FromStr};
 
 use actix_files::NamedFile;
 use actix_web::{
-    get, http::StatusCode, middleware::Logger, post, web, App, HttpRequest, HttpResponse,
+    error::InternalError, get, http::StatusCode, middleware::Logger, post, web, App, HttpRequest, HttpResponse,
     HttpServer, Responder,
 };
 use actix_web_actors::ws;
@@ -58,21 +58,22 @@ struct DownloadRequest {
     download: Option<download::DownloadSelection>,
 }
 
-#[derive(Template)]
+#[derive(Serialize, Template)]
 #[template(path = "download.html")]
-struct DownloadInfo<'a> {
+struct DownloadInfo {
     file: StoredFile,
-    code: &'a str,
+    code: String,
     available: u64,
+    offsets: Option<Vec<u64>>,
 }
 
 #[get("/download")]
 async fn handle_download(
     req: HttpRequest,
-    download: web::Query<DownloadRequest>,
+    query: web::Query<DownloadRequest>,
     data: web::Data<AppState>,
 ) -> actix_web::Result<HttpResponse> {
-    let code = &download.code;
+    let code = &query.code;
     if !store::is_valid_storage_code(code) {
         return not_found(req, data, true);
     }
@@ -85,7 +86,7 @@ async fn handle_download(
 
     let storage_path = data.config.storage_dir.join(code);
     let file = File::open(&storage_path).await?;
-    if let Some(selection) = download.download {
+    if let Some(selection) = query.download {
         if let download::DownloadSelection::One(n) = selection {
             if let Some(ref files) = info.contents {
                 if n >= files.len() {
@@ -103,26 +104,60 @@ async fn handle_download(
         }
            .into_response(&req))
     } else {
+        let offsets = info.contents.as_deref().map(zip::file_data_offsets);
         Ok(HttpResponse::Ok().body(DownloadInfo {
             file: info,
-            code,
+            code: code.clone(),
             available: file.metadata().await?.len(),
+            offsets,
         }.render().unwrap()))
     }
 }
 
-fn not_found(
+#[derive(Deserialize)]
+struct InfoQuery {
+    code: String,
+}
+
+#[get("/info")]
+async fn download_info(
+    req: HttpRequest,
+    query: web::Query<InfoQuery>,
+    data: web::Data<AppState>,
+) -> actix_web::Result<impl Responder> {
+    let code = &query.code;
+    if !store::is_valid_storage_code(code) {
+        return not_found(req, data, true);
+    }
+    let info = data.file_store.read().await.lookup_file(code);
+    let info = if let Some(i) = info {
+        i
+    } else {
+        return not_found(req, data, true)
+    };
+
+    let storage_path = data.config.storage_dir.join(code);
+    let offsets = info.contents.as_deref().map(zip::file_data_offsets);
+    Ok(web::Json(DownloadInfo {
+        file: info,
+        code: code.clone(),
+        available: File::open(&storage_path).await?.metadata().await?.len(),
+        offsets,
+    }))
+}
+
+fn not_found<T>(
     req: HttpRequest,
     data: web::Data<AppState>,
     report: bool,
-) -> actix_web::Result<HttpResponse> {
+) -> actix_web::Result<T> {
     if report {
         let ip_addr = get_ip_addr(&req, data.config.reverse_proxy);
         log_auth_failure(&ip_addr);
     }
-    Ok(NamedFile::open(data.config.static_dir.join("404.html"))?
+    Err(InternalError::from_response("Download not found", NamedFile::open(data.config.static_dir.join("404.html"))?
         .set_status_code(StatusCode::NOT_FOUND)
-        .into_response(&req))
+        .into_response(&req)).into())
 }
 
 #[get("/upload")]
@@ -244,6 +279,7 @@ async fn main() -> std::io::Result<()> {
                 Logger::default()
             })
             .service(handle_download)
+            .service(download_info)
             .service(handle_upload)
             .service(check_upload_password)
             .service(upload_limits)
diff --git a/src/zip.rs b/src/zip.rs
index c0001e8..3160e84 100644
--- a/src/zip.rs
+++ b/src/zip.rs
@@ -43,6 +43,17 @@ pub fn file_data_offset(files: &[UploadedFile], idx: usize) -> u64 {
         + files[idx].name.len() as u64
 }
 
+pub fn file_data_offsets(files: &[UploadedFile]) -> Vec<u64> {
+    let mut offsets = Vec::new();
+    let mut offset: u64 = 0;
+    for file in files.iter() {
+        offset += LOCAL_HEADER_SIZE_MINUS_FILENAME + file.name.len() as u64;
+        offsets.push(offset);
+        offset += file.size + DATA_DESCRIPTOR_SIZE;
+    }
+    offsets
+}
+
 fn central_directory_size(files: &[UploadedFile]) -> u64 {
     let mut total = 0;
     for file in files.iter() {
diff --git a/static/js/download.js b/static/js/download.js
new file mode 100644
index 0000000..ccd1168
--- /dev/null
+++ b/static/js/download.js
@@ -0,0 +1,14 @@
+document.addEventListener("DOMContentLoaded", () => {
+    const table = document.getElementById("download_contents").getElementsByTagName("tbody")[0];
+    if (table.children.length === 0) { return; }
+
+    setInterval(() => {
+        fetch(`info?code=${CODE}`)
+            .then((res) => res.json())
+            .then((info) => {
+                for (const [index, offset] of info.offsets.entries()) {
+                    table.children[index].className = (offset > info.available) ? "unavailable" : "";
+                }
+            });
+    }, 5000);
+});
diff --git a/templates/download.html b/templates/download.html
index 413cca4..f282db2 100644
--- a/templates/download.html
+++ b/templates/download.html
@@ -4,10 +4,12 @@
     <meta charset="utf-8"/>
     <meta name="viewport" content="width=device-width, initial-scale=1"/>
     <link rel="stylesheet" type="text/css" href="css/transbeam.css"/>
-    <link rel="stylesheet" type="text/css" href="css/download.css"/>
     <link rel="apple-touch-icon" href="images/site-icons/transbeam-apple.png"/>
     <link rel="manifest" href="manifest.json"/>
     <script src="js/util.js"></script>
+    <script type="text/javascript">
+      const CODE = "{{ code }}";
+    </script>
     <script src="js/download.js"></script>
     <title>{{ file.name }} - transbeam</title>
   </head>
@@ -25,16 +27,17 @@
       {% when Some with (files) %}
         <div id="download_contents" class="section">
           <h3>Contents</h3>
-          <table>
+          <table><tbody>
+            {% let offsets = offsets.as_ref().unwrap() %}
             {% for f in files %}
-              <tr class="{% if zip::file_data_offset(files.as_ref(), loop.index0.clone()) > available %}unavailable{% endif %}">
+              <tr class="{% if offsets.get(loop.index0.clone()).unwrap().clone() > available %}unavailable{% endif %}">
                 <td class="file_size">{{ bytesize::to_string(f.size.clone(), false).replace(" ", "") }}</td>
                 <td class="file_name">{{ f.name }}</td>
                 <td class="file_download"><a class="download_button" href="download?code={{ code }}&download={{ loop.index0 }}"></a></td>
                 <td class="file_unavailable"></td>
               </tr>
             {% endfor %}
-          </table>
+          </tbody></table>
         </div>
       {% else %}
     {% endmatch %}