diff --git a/src/app/components/FileManager.tsx b/src/app/components/FileManager.tsx
index 64df6c0..98ad9b8 100644
--- a/src/app/components/FileManager.tsx
+++ b/src/app/components/FileManager.tsx
@@ -43,6 +43,7 @@ import {
   createFolder,
   deletePath,
   getFileContents,
+  getFileRange,
   humanFileSize,
   joinPath,
   listDirectory,
@@ -197,14 +198,16 @@ function MarkdownEditor({ text, onSave }: { text: string; onSave?: (s: string) =
   return (
     <div className="flex flex-col h-full">
       <div className="flex items-center gap-2 px-3 py-1.5 bg-neutral-900 border-b border-neutral-700 flex-shrink-0 text-xs">
-        <button
-          onClick={() => setEditMode(v => !v)}
-          className={editMode
-            ? 'px-2 py-1 rounded bg-amber-600 text-white inline-flex items-center gap-1'
-            : 'px-2 py-1 rounded bg-neutral-700 text-neutral-300 hover:bg-neutral-600 inline-flex items-center gap-1'}
-        >
-          {editMode ? <><Eye className="w-3.5 h-3.5" /> View</> : <><Pencil className="w-3.5 h-3.5" /> Edit</>}
-        </button>
+        {onSave && (
+          <button
+            onClick={() => setEditMode(v => !v)}
+            className={editMode
+              ? 'px-2 py-1 rounded bg-amber-600 text-white inline-flex items-center gap-1'
+              : 'px-2 py-1 rounded bg-neutral-700 text-neutral-300 hover:bg-neutral-600 inline-flex items-center gap-1'}
+          >
+            {editMode ? <><Eye className="w-3.5 h-3.5" /> View</> : <><Pencil className="w-3.5 h-3.5" /> Edit</>}
+          </button>
+        )}
         {editMode && onSave && (
           <button onClick={() => void save()} disabled={saving}
             className="px-2 py-1 rounded bg-blue-600 text-white hover:bg-blue-700 disabled:opacity-50 inline-flex items-center gap-1">
@@ -276,6 +279,11 @@ export default function FileManager({ initialPath = '/', config, setConfig, onBa
   const [viewImgUrl, setViewImgUrl] = useState<string | null>(null);
   const [viewHexData, setViewHexData] = useState<Uint8Array | null>(null);
   const [viewLoading, setViewLoading] = useState(false);
+  const [viewOffset, setViewOffset] = useState(0);
+  const [bufferSize, setBufferSize] = useState<number>(() => {
+    const v = Number(localStorage.getItem('fileManager.bufferSize'));
+    return v > 0 ? v : 65536;
+  });
 
   // Rename / folder
   const [showNewFolder, setShowNewFolder] = useState(false);
@@ -353,6 +361,24 @@ export default function FileManager({ initialPath = '/', config, setConfig, onBa
     else                       setViewText(await blob.text());
   };
 
+  // Fetch a buffer window and populate viewer state.
+  // For images always loads the full file; everything else uses Range requests.
+  const loadBuffer = async (entry: EntryInfo, offset: number, mode: ViewMode, size = bufferSize) => {
+    let blob: Blob;
+    if (mode === 'image') {
+      blob = await getFileContents(entry.path);
+      setViewOffset(0);
+    } else {
+      const fileSize = entry.size;
+      const clampedOffset = fileSize > 0 ? Math.max(0, Math.min(offset, fileSize - 1)) : Math.max(0, offset);
+      const rangeEnd = fileSize > 0 ? Math.min(clampedOffset + size - 1, fileSize - 1) : clampedOffset + size - 1;
+      blob = await getFileRange(entry.path, clampedOffset, rangeEnd);
+      setViewOffset(clampedOffset);
+    }
+    setViewBlob(blob);
+    await processBlob(blob, mode);
+  };
+
   const openEntry = async (entry: EntryInfo, mode?: ViewMode) => {
     if (renameEntry !== null) return;
     if (entry.type === 'folder') { navigateTo(joinPath(path, entry.name)); return; }
@@ -363,11 +389,10 @@ export default function FileManager({ initialPath = '/', config, setConfig, onBa
     setViewText(null);
     setViewImgUrl(null);
     setViewHexData(null);
+    setViewOffset(0);
     setViewLoading(true);
     try {
-      const blob = await getFileContents(entry.path);
-      setViewBlob(blob);
-      await processBlob(blob, targetMode);
+      await loadBuffer(entry, 0, targetMode);
     } catch (e: any) {
       toast.error(`Failed to open ${entry.name}: ${e?.message ?? e}`);
       setViewEntry(null);
@@ -378,16 +403,41 @@ export default function FileManager({ initialPath = '/', config, setConfig, onBa
   };
 
   const switchViewMode = async (mode: ViewMode) => {
-    if (!viewBlob) return;
+    if (!viewEntry) return;
     setViewMode(mode);
     setViewLoading(true);
-    try { await processBlob(viewBlob, mode); } finally { setViewLoading(false); }
+    try { await loadBuffer(viewEntry, viewOffset, mode); } finally { setViewLoading(false); }
+  };
+
+  const prevBuffer = async () => {
+    if (!viewEntry || !viewMode || viewOffset <= 0) return;
+    setViewLoading(true);
+    try { await loadBuffer(viewEntry, Math.max(0, viewOffset - bufferSize), viewMode); }
+    finally { setViewLoading(false); }
+  };
+
+  const nextBuffer = async () => {
+    if (!viewEntry || !viewMode) return;
+    if (viewEntry.size > 0 && viewOffset + bufferSize >= viewEntry.size) return;
+    setViewLoading(true);
+    try { await loadBuffer(viewEntry, viewOffset + bufferSize, viewMode); }
+    finally { setViewLoading(false); }
+  };
+
+  const changeBufferSize = async (newSize: number) => {
+    localStorage.setItem('fileManager.bufferSize', String(newSize));
+    setBufferSize(newSize);
+    if (!viewEntry || !viewMode || viewMode === 'image') return;
+    const aligned = Math.floor(viewOffset / newSize) * newSize;
+    setViewLoading(true);
+    try { await loadBuffer(viewEntry, aligned, viewMode, newSize); }
+    finally { setViewLoading(false); }
   };
 
   const closeViewer = () => {
     setViewImgUrl(prev => { if (prev) URL.revokeObjectURL(prev); return null; });
     setViewEntry(null); setViewMode(null); setViewBlob(null);
-    setViewText(null);  setViewHexData(null);
+    setViewText(null);  setViewHexData(null); setViewOffset(0);
   };
 
   const saveViewFile = async (content: string | Uint8Array) => {
@@ -930,59 +980,104 @@ export default function FileManager({ initialPath = '/', config, setConfig, onBa
       </Dialog>
 
       {/* ── File viewer overlay ── */}
-      {viewEntry && (
-        <div className="fixed inset-0 bg-neutral-950 z-50 flex flex-col">
-          <div className="bg-neutral-900 flex items-center px-4 py-2 gap-3 border-b border-neutral-700 flex-shrink-0">
-            <button onClick={closeViewer} className="p-1.5 rounded hover:bg-neutral-700">
-              <X className="w-5 h-5 text-white" />
-            </button>
-            <span className="font-medium truncate flex-1 text-sm text-white">{viewEntry.name}</span>
-            {/* Mode switcher */}
-            <div className="flex items-center gap-1">
-              {viewMode && availableViewers(viewEntry).map(mode => (
-                <button
-                  key={mode}
-                  onClick={() => void switchViewMode(mode)}
-                  title={VIEWER_LABEL[mode]}
-                  className={`px-2 py-1 rounded text-xs inline-flex items-center gap-1 transition-colors ${
-                    viewMode === mode
-                      ? 'bg-blue-600 text-white'
-                      : 'text-neutral-400 hover:bg-neutral-700 hover:text-white'
-                  }`}
-                >
-                  <ViewerModeIcon mode={mode} className="w-3.5 h-3.5" />
-                  <span className="hidden sm:inline">{VIEWER_LABEL[mode]}</span>
-                </button>
-              ))}
-            </div>
-            <button onClick={() => void downloadEntry(viewEntry)} className="p-1.5 rounded hover:bg-neutral-700 text-neutral-300 hover:text-white" title="Download">
-              <Download className="w-4 h-4" />
-            </button>
-          </div>
+      {viewEntry && (() => {
+        const fileSize = viewEntry.size;
+        const isFullyLoaded = fileSize === 0 || fileSize <= bufferSize;
+        const windowEnd = fileSize > 0 ? Math.min(viewOffset + bufferSize, fileSize) : viewOffset + bufferSize;
+        const hasPrev = viewOffset > 0;
+        const hasNext = fileSize > 0 ? viewOffset + bufferSize < fileSize : false;
 
-          <div className="flex-1 overflow-hidden bg-neutral-950">
-            {viewLoading && (
-              <div className="h-full flex items-center justify-center gap-2 text-neutral-400">
-                <Loader2 className="w-5 h-5 animate-spin" /> Loading…
+        return (
+          <div className="fixed inset-0 bg-neutral-950 z-50 flex flex-col">
+            {/* Title + mode switcher */}
+            <div className="bg-neutral-900 flex items-center px-4 py-2 gap-3 border-b border-neutral-700 flex-shrink-0">
+              <button onClick={closeViewer} className="p-1.5 rounded hover:bg-neutral-700">
+                <X className="w-5 h-5 text-white" />
+              </button>
+              <span className="font-medium truncate flex-1 text-sm text-white">{viewEntry.name}</span>
+              <div className="flex items-center gap-1">
+                {viewMode && availableViewers(viewEntry).map(mode => (
+                  <button
+                    key={mode}
+                    onClick={() => void switchViewMode(mode)}
+                    title={VIEWER_LABEL[mode]}
+                    className={`px-2 py-1 rounded text-xs inline-flex items-center gap-1 transition-colors ${
+                      viewMode === mode
+                        ? 'bg-blue-600 text-white'
+                        : 'text-neutral-400 hover:bg-neutral-700 hover:text-white'
+                    }`}
+                  >
+                    <ViewerModeIcon mode={mode} className="w-3.5 h-3.5" />
+                    <span className="hidden sm:inline">{VIEWER_LABEL[mode]}</span>
+                  </button>
+                ))}
+              </div>
+              <button onClick={() => void downloadEntry(viewEntry)} className="p-1.5 rounded hover:bg-neutral-700 text-neutral-300 hover:text-white" title="Download">
+                <Download className="w-4 h-4" />
+              </button>
+            </div>
+
+            {/* Buffer navigation bar (hidden for images) */}
+            {viewMode !== 'image' && (
+              <div className="bg-neutral-800 px-3 py-1.5 border-b border-neutral-700 flex items-center gap-2 text-xs flex-shrink-0">
+                <button
+                  onClick={() => void prevBuffer()}
+                  disabled={!hasPrev || viewLoading}
+                  className="px-2 py-0.5 rounded bg-neutral-700 text-neutral-300 hover:bg-neutral-600 disabled:opacity-30 disabled:cursor-default"
+                >
+                  ‹ Prev
+                </button>
+                <span className="text-neutral-400 flex-1 text-center tabular-nums">
+                  {fileSize > 0
+                    ? `${viewOffset.toLocaleString()} – ${windowEnd.toLocaleString()} of ${fileSize.toLocaleString()} bytes`
+                    : `offset ${viewOffset.toLocaleString()}`}
+                </span>
+                <button
+                  onClick={() => void nextBuffer()}
+                  disabled={!hasNext || viewLoading}
+                  className="px-2 py-0.5 rounded bg-neutral-700 text-neutral-300 hover:bg-neutral-600 disabled:opacity-30 disabled:cursor-default"
+                >
+                  Next ›
+                </button>
+                <span className="text-neutral-600 ml-2">Buffer</span>
+                <select
+                  value={bufferSize}
+                  onChange={e => void changeBufferSize(Number(e.target.value))}
+                  className="bg-neutral-700 text-neutral-300 rounded px-1.5 py-0.5 border-0 focus:outline-none"
+                >
+                  <option value={4096}>4 KB</option>
+                  <option value={16384}>16 KB</option>
+                  <option value={65536}>64 KB</option>
+                  <option value={262144}>256 KB</option>
+                  <option value={1048576}>1 MB</option>
+                </select>
               </div>
             )}
-            {!viewLoading && viewMode === 'image' && viewImgUrl && (
-              <div className="h-full flex items-center justify-center overflow-auto p-4">
-                <img src={viewImgUrl} alt={viewEntry.name} className="max-w-full max-h-full object-contain" />
-              </div>
-            )}
-            {!viewLoading && viewMode === 'hex' && viewHexData && (
-              <HexEditor data={viewHexData} onSave={d => saveViewFile(d)} />
-            )}
-            {!viewLoading && viewMode === 'markdown' && viewText !== null && (
-              <MarkdownEditor text={viewText} onSave={s => saveViewFile(s)} />
-            )}
-            {!viewLoading && (viewMode === 'text' || viewMode === 'json' || viewMode === 'xml') && viewText !== null && (
-              <CodeEditor text={viewText} mode={viewMode} onSave={s => saveViewFile(s)} />
-            )}
+
+            <div className="flex-1 overflow-hidden bg-neutral-950">
+              {viewLoading && (
+                <div className="h-full flex items-center justify-center gap-2 text-neutral-400">
+                  <Loader2 className="w-5 h-5 animate-spin" /> Loading…
+                </div>
+              )}
+              {!viewLoading && viewMode === 'image' && viewImgUrl && (
+                <div className="h-full flex items-center justify-center overflow-auto p-4">
+                  <img src={viewImgUrl} alt={viewEntry.name} className="max-w-full max-h-full object-contain" />
+                </div>
+              )}
+              {!viewLoading && viewMode === 'hex' && viewHexData && (
+                <HexEditor data={viewHexData} readOnly={!isFullyLoaded} onSave={isFullyLoaded ? d => saveViewFile(d) : undefined} />
+              )}
+              {!viewLoading && viewMode === 'markdown' && viewText !== null && (
+                <MarkdownEditor text={viewText} onSave={isFullyLoaded ? s => saveViewFile(s) : undefined} />
+              )}
+              {!viewLoading && (viewMode === 'text' || viewMode === 'json' || viewMode === 'xml') && viewText !== null && (
+                <CodeEditor text={viewText} mode={viewMode} readOnly={!isFullyLoaded} onSave={isFullyLoaded ? s => saveViewFile(s) : undefined} />
+              )}
+            </div>
           </div>
-        </div>
-      )}
+        );
+      })()}
 
       {/* ── Mount dialog ── */}
       <Dialog open={mountEntry !== null} onOpenChange={open => !open && setMountEntry(null)}>
diff --git a/src/app/webdav.ts b/src/app/webdav.ts
index 4f1b58c..e2263a3 100644
--- a/src/app/webdav.ts
+++ b/src/app/webdav.ts
@@ -317,6 +317,19 @@ export async function getFileContents(path: string): Promise<Blob> {
   return r.blob();
 }
 
+/**
+ * Fetch a byte range of a file using HTTP Range requests.
+ * Returns a Blob containing the requested bytes. Falls back to a full
+ * fetch if the server responds 200 (no Range support).
+ */
+export async function getFileRange(path: string, start: number, end: number): Promise<Blob> {
+  const base = getWebDAVClient().client.baseUrl;
+  const url  = pathToUrl(normalizePath(path), base);
+  const r    = await fetch(url, { headers: { Range: `bytes=${start}-${end}` } });
+  if (r.status === 206 || r.status === 200) return r.blob();
+  throw new Error(`GET range failed: ${r.status} ${r.statusText}`);
+}
+
 // ----- Helpers --------------------------------------------------------
 
 /** Convert a server-relative path to an absolute URL on the configured base. */