diff --git a/src/download.rs b/src/download.rs
index 21fabda..aad73e8 100644
--- a/src/download.rs
+++ b/src/download.rs
@@ -16,8 +16,8 @@ use inotify::{Inotify, WatchMask};
 use log::trace;
 use pin_project_lite::pin_project;
 use serde::{de, Deserialize, Deserializer};
-use time::OffsetDateTime;
 use std::{os::unix::fs::MetadataExt, time::SystemTime};
+use time::OffsetDateTime;
 
 use actix_web::{
     body::{self, BoxBody, SizedStream},
@@ -64,7 +64,9 @@ impl<'de> de::Visitor<'de> for SelectionVisitor {
     }
 
     fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
-    where E: de::Error {
+    where
+        E: de::Error,
+    {
         if v == "all" {
             Ok(DownloadSelection::All)
         } else if let Ok(n) = v.parse::<usize>() {
@@ -76,9 +78,7 @@ impl<'de> de::Visitor<'de> for SelectionVisitor {
 }
 
 impl<'de> Deserialize<'de> for DownloadSelection {
-    fn deserialize<D: Deserializer<'de>>(
-        de: D
-    ) -> Result<DownloadSelection, D::Error> {
+    fn deserialize<D: Deserializer<'de>>(de: D) -> Result<DownloadSelection, D::Error> {
         de.deserialize_any(SelectionVisitor)
     }
 }
@@ -122,8 +122,10 @@ impl DownloadingFile {
     }
 
     fn baseline_offset(&self) -> u64 {
-        if let (DownloadSelection::One(n), Some(files)) = (self.selection, self.info.contents.as_ref()) {
-            crate::zip::file_data_offset(&files, n)
+        if let (DownloadSelection::One(n), Some(files)) =
+            (self.selection, self.info.contents.as_ref())
+        {
+            crate::zip::file_data_offset(files, n)
         } else {
             0
         }
@@ -184,12 +186,7 @@ impl DownloadingFile {
 
                     res.insert_header((
                         header::CONTENT_RANGE,
-                        format!(
-                            "bytes {}-{}/{}",
-                            offset,
-                            offset + length - 1,
-                            total_size,
-                        ),
+                        format!("bytes {}-{}/{}", offset, offset + length - 1, total_size,),
                     ));
                 } else {
                     res.insert_header((header::CONTENT_RANGE, format!("bytes */{}", length)));
@@ -209,7 +206,12 @@ impl DownloadingFile {
                 .map_into_boxed_body();
         }
 
-        let reader = new_live_reader(length, self.baseline_offset() + offset, self.file, self.storage_path);
+        let reader = new_live_reader(
+            length,
+            self.baseline_offset() + offset,
+            self.file,
+            self.storage_path,
+        );
 
         if offset != 0 || length != total_size {
             res.status(StatusCode::PARTIAL_CONTENT);
diff --git a/src/main.rs b/src/main.rs
index 5eb24f5..2fa3456 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,8 +8,8 @@ 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,
-    HttpServer, Responder,
+    error::InternalError, get, http::StatusCode, middleware::Logger, post, web, App, HttpRequest,
+    HttpResponse, HttpServer, Responder,
 };
 use actix_web_actors::ws;
 use askama::Template;
@@ -51,28 +51,28 @@ pub fn log_auth_failure(ip_addr: &str) {
     warn!("Incorrect authentication attempt from {}", ip_addr);
 }
 
-
 #[derive(Deserialize)]
 struct DownloadRequest {
     code: String,
     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);
     }
@@ -80,12 +80,12 @@ async fn handle_download(
     let info = if let Some(i) = info {
         i
     } else {
-        return not_found(req, data, true)
+        return not_found(req, data, true);
     };
 
     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() {
@@ -101,28 +101,66 @@ async fn handle_download(
             info,
             selection,
         }
-           .into_response(&req))
+        .into_response(&req))
     } else {
-        Ok(HttpResponse::Ok().body(DownloadInfo {
-            file: info,
-            code,
-            available: file.metadata().await?.len(),
-        }.render().unwrap()))
+        let offsets = info.contents.as_deref().map(zip::file_data_offsets);
+        Ok(HttpResponse::Ok().body(
+            DownloadInfo {
+                file: info,
+                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>,
-    report: bool,
-) -> actix_web::Result<HttpResponse> {
+) -> 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<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"))?
-        .set_status_code(StatusCode::NOT_FOUND)
-        .into_response(&req))
+    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())
 }
 
 #[get("/upload")]
@@ -244,6 +282,7 @@ 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/timestamp.rs b/src/timestamp.rs
index fb79450..8ee8a82 100644
--- a/src/timestamp.rs
+++ b/src/timestamp.rs
@@ -3,10 +3,7 @@ use core::fmt;
 use serde::{de::Visitor, Deserializer, Serializer};
 use time::OffsetDateTime;
 
-pub(crate) fn serialize<S: Serializer>(
-    time: &OffsetDateTime,
-    ser: S,
-) -> Result<S::Ok, S::Error> {
+pub(crate) fn serialize<S: Serializer>(time: &OffsetDateTime, ser: S) -> Result<S::Ok, S::Error> {
     ser.serialize_i64(time.unix_timestamp())
 }
 
@@ -28,9 +25,7 @@ impl<'de> Visitor<'de> for I64Visitor {
     }
 }
 
-pub(crate) fn deserialize<'de, D: Deserializer<'de>>(
-    de: D,
-) -> Result<OffsetDateTime, D::Error> {
+pub(crate) fn deserialize<'de, D: Deserializer<'de>>(de: D) -> Result<OffsetDateTime, D::Error> {
     Ok(
         OffsetDateTime::from_unix_timestamp(de.deserialize_i64(I64Visitor)?)
             .unwrap_or_else(|_| OffsetDateTime::now_utc()),
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/css/transbeam.css b/static/css/transbeam.css
index 48d38ba..a8d0792 100644
--- a/static/css/transbeam.css
+++ b/static/css/transbeam.css
@@ -4,6 +4,7 @@ body {
     max-width: 512px;
     margin: 0.5em auto;
     padding: 0 1em;
+    overflow-wrap: break-word;
 }
 
 #header h1 {
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 %}