diff --git a/shared/static/scripts/sx.js b/shared/static/scripts/sx.js
index 0ecf760..43ac749 100644
--- a/shared/static/scripts/sx.js
+++ b/shared/static/scripts/sx.js
@@ -1342,9 +1342,56 @@
         var text = s.textContent;
         if (!text || !text.trim()) continue;
 
-        // data-components: load as component definitions
+        // data-components: load as component definitions (with localStorage caching)
         if (s.hasAttribute("data-components")) {
-          Sx.loadComponents(text);
+          var hash = s.getAttribute("data-hash");
+          if (hash) {
+            var hasInline = text && text.trim();
+            try {
+              var cachedHash = localStorage.getItem("sx-components-hash");
+              if (cachedHash === hash) {
+                // Cache hit
+                if (hasInline) {
+                  // Server sent full source (cookie was missing/stale) — update cache
+                  localStorage.setItem("sx-components-src", text);
+                  Sx.loadComponents(text);
+                } else {
+                  // Server omitted source — load from cache
+                  var cached = localStorage.getItem("sx-components-src");
+                  if (cached) {
+                    Sx.loadComponents(cached);
+                  } else {
+                    // Cache entry missing — clear cookie and reload to get full source
+                    _clearSxCompCookie();
+                    location.reload();
+                    return;
+                  }
+                }
+              } else {
+                // Cache miss — hash mismatch
+                if (hasInline) {
+                  // Server sent full source — parse and cache
+                  localStorage.setItem("sx-components-hash", hash);
+                  localStorage.setItem("sx-components-src", text);
+                  Sx.loadComponents(text);
+                } else {
+                  // Server omitted source but our cache is stale — clear and reload
+                  localStorage.removeItem("sx-components-hash");
+                  localStorage.removeItem("sx-components-src");
+                  _clearSxCompCookie();
+                  location.reload();
+                  return;
+                }
+              }
+            } catch (e) {
+              // localStorage unavailable — fall back to inline
+              if (hasInline) Sx.loadComponents(text);
+            }
+            _setSxCompCookie(hash);
+          } else {
+            // Legacy: no hash attribute — just load inline
+            if (text && text.trim()) Sx.loadComponents(text);
+          }
           continue;
         }
 
@@ -2396,6 +2443,18 @@
     return text;
   }
 
+  // ---------------------------------------------------------------------------
+  // sx-comp-hash cookie helpers (component caching)
+  // ---------------------------------------------------------------------------
+
+  function _setSxCompCookie(hash) {
+    document.cookie = "sx-comp-hash=" + hash + ";path=/;max-age=31536000;SameSite=Lax";
+  }
+
+  function _clearSxCompCookie() {
+    document.cookie = "sx-comp-hash=;path=/;max-age=0;SameSite=Lax";
+  }
+
   if (typeof document !== "undefined") {
     var init = function () {
       console.log("[sx.js] v" + Sx.VERSION + " init");
diff --git a/shared/sx/helpers.py b/shared/sx/helpers.py
index 69f48bb..8c0f827 100644
--- a/shared/sx/helpers.py
+++ b/shared/sx/helpers.py
@@ -483,7 +483,7 @@ details.group{{overflow:hidden}}details.group>summary{{list-style:none}}details.
 </style>
 </head>
 <body class="bg-stone-50 text-stone-900">
-<script type="text/sx" data-components>{component_defs}</script>
+<script type="text/sx" data-components data-hash="{component_hash}">{component_defs}</script>
 <script type="text/sx" data-mount="body">{page_sx}</script>
 <script src="{asset_url}/scripts/sx.js?v={sx_js_hash}"></script>
 <script src="{asset_url}/scripts/body.js?v={body_js_hash}"></script>
@@ -499,19 +499,26 @@ def sx_page(ctx: dict, page_sx: str, *,
     renders everything client-side.  CSS rules are scanned from the sx
     source and component defs, then injected as a <style> block.
     """
-    from .jinja_bridge import client_components_tag, _COMPONENT_ENV
+    from .jinja_bridge import client_components_tag, _COMPONENT_ENV, get_component_hash
     from .css_registry import scan_classes_from_sx, lookup_rules, get_preamble, registry_loaded, store_css_hash
     from .types import Component
 
-    components_tag = client_components_tag()
-    # Extract just the inner source from the <script> tag
-    component_defs = ""
-    if components_tag:
-        # Strip <script type="text/sx" data-components>...</script>
-        start = components_tag.find(">") + 1
-        end = components_tag.rfind("</script>")
-        if start > 0 and end > start:
-            component_defs = components_tag[start:end]
+    component_hash = get_component_hash()
+
+    # Check if client already has this version cached (via cookie)
+    client_hash = _get_sx_comp_cookie()
+    if client_hash and client_hash == component_hash:
+        # Client has current components cached — send empty source
+        component_defs = ""
+    else:
+        components_tag = client_components_tag()
+        # Extract just the inner source from the <script> tag
+        component_defs = ""
+        if components_tag:
+            start = components_tag.find(">") + 1
+            end = components_tag.rfind("</script>")
+            if start > 0 and end > start:
+                component_defs = components_tag[start:end]
 
     # Scan for CSS classes — use pre-computed sets for components, scan page sx at request time
     sx_css = ""
@@ -543,6 +550,7 @@ def sx_page(ctx: dict, page_sx: str, *,
         asset_url=asset_url,
         meta_html=meta_html,
         csrf=_html_escape(csrf),
+        component_hash=component_hash,
         component_defs=component_defs,
         page_sx=page_sx,
         sx_css=sx_css,
@@ -575,6 +583,15 @@ def _get_csrf_token() -> str:
         return ""
 
 
+def _get_sx_comp_cookie() -> str:
+    """Read the sx-comp-hash cookie from the current request."""
+    try:
+        from quart import request
+        return request.cookies.get("sx-comp-hash", "")
+    except Exception:
+        return ""
+
+
 def _html_escape(s: str) -> str:
     """Minimal HTML escaping for attribute values."""
     return (s.replace("&", "&amp;")
diff --git a/shared/sx/jinja_bridge.py b/shared/sx/jinja_bridge.py
index 647aa44..f6025a9 100644
--- a/shared/sx/jinja_bridge.py
+++ b/shared/sx/jinja_bridge.py
@@ -21,6 +21,7 @@ Setup::
 from __future__ import annotations
 
 import glob
+import hashlib
 import os
 from typing import Any
 
@@ -37,12 +38,42 @@ from .html import render as html_render, _render_component
 # definition files or calling register_components().
 _COMPONENT_ENV: dict[str, Any] = {}
 
+# SHA-256 hash (12 hex chars) of all component definitions — used for
+# client-side localStorage caching.
+_COMPONENT_HASH: str = ""
+
 
 def get_component_env() -> dict[str, Any]:
     """Return the shared component environment."""
     return _COMPONENT_ENV
 
 
+def get_component_hash() -> str:
+    """Return the current component definitions hash."""
+    return _COMPONENT_HASH
+
+
+def _compute_component_hash() -> None:
+    """Recompute _COMPONENT_HASH from all registered Component definitions."""
+    global _COMPONENT_HASH
+    from .parser import serialize
+    parts = []
+    for key in sorted(_COMPONENT_ENV):
+        val = _COMPONENT_ENV[key]
+        if isinstance(val, Component):
+            param_strs = ["&key"] + list(val.params)
+            if val.has_children:
+                param_strs.extend(["&rest", "children"])
+            params_sx = "(" + " ".join(param_strs) + ")"
+            body_sx = serialize(val.body)
+            parts.append(f"(defcomp ~{val.name} {params_sx} {body_sx})")
+    if parts:
+        digest = hashlib.sha256("\n".join(parts).encode()).hexdigest()[:12]
+        _COMPONENT_HASH = digest
+    else:
+        _COMPONENT_HASH = ""
+
+
 def load_sx_dir(directory: str) -> None:
     """Load all .sx files from a directory and register components."""
     for filepath in sorted(
@@ -132,6 +163,8 @@ def register_components(sx_source: str) -> None:
                 all_classes = scan_classes_from_sx(sx_source)
             val.css_classes = set(all_classes)
 
+    _compute_component_hash()
+
 
 # ---------------------------------------------------------------------------
 # sx() — render s-expression from Jinja template
