diff --git a/shared/sx/deps.py b/shared/sx/deps.py
new file mode 100644
index 0000000..31a53ad
--- /dev/null
+++ b/shared/sx/deps.py
@@ -0,0 +1,114 @@
+"""
+Component dependency analysis.
+
+Walks component AST bodies to compute transitive dependency sets.
+A component's deps are all other components (~name references) it
+can potentially render, including through control flow branches.
+"""
+from __future__ import annotations
+
+from typing import Any
+
+from .types import Component, Macro, Symbol
+
+
+def _scan_ast(node: Any) -> set[str]:
+    """Scan an AST node for ~component references.
+
+    Walks all branches of control flow (if/when/cond/case) to find
+    every component that *could* be rendered.  Returns a set of
+    component names (with ~ prefix).
+    """
+    refs: set[str] = set()
+    _walk(node, refs)
+    return refs
+
+
+def _walk(node: Any, refs: set[str]) -> None:
+    """Recursively walk an AST node collecting ~name references."""
+    if isinstance(node, Symbol):
+        if node.name.startswith("~"):
+            refs.add(node.name)
+        return
+
+    if isinstance(node, list):
+        for item in node:
+            _walk(item, refs)
+        return
+
+    if isinstance(node, dict):
+        for v in node.values():
+            _walk(v, refs)
+        return
+
+    # Literals (str, int, float, bool, None, Keyword) — no refs
+    return
+
+
+def transitive_deps(name: str, env: dict[str, Any]) -> set[str]:
+    """Compute transitive component dependencies for *name*.
+
+    Returns the set of all component names (with ~ prefix) that
+    *name* can transitively render, NOT including *name* itself.
+    """
+    seen: set[str] = set()
+
+    def walk(n: str) -> None:
+        if n in seen:
+            return
+        seen.add(n)
+        val = env.get(n)
+        if isinstance(val, Component):
+            for dep in _scan_ast(val.body):
+                walk(dep)
+        elif isinstance(val, Macro):
+            for dep in _scan_ast(val.body):
+                walk(dep)
+
+    key = name if name.startswith("~") else f"~{name}"
+    walk(key)
+    return seen - {key}
+
+
+def compute_all_deps(env: dict[str, Any]) -> None:
+    """Compute and cache deps for all Component entries in *env*.
+
+    Mutates each Component's ``deps`` field in place.
+    """
+    for key, val in env.items():
+        if isinstance(val, Component):
+            val.deps = transitive_deps(key, env)
+
+
+def scan_components_from_sx(source: str) -> set[str]:
+    """Extract component names referenced in SX source text.
+
+    Uses regex to find (~name patterns in serialized SX wire format.
+    Returns names with ~ prefix, e.g. {"~card", "~nav-link"}.
+    """
+    import re
+    return set(re.findall(r'\(~([a-zA-Z_][a-zA-Z0-9_\-]*)', source))
+
+
+def components_needed(page_sx: str, env: dict[str, Any]) -> set[str]:
+    """Compute the full set of component names needed for a page.
+
+    Scans *page_sx* for direct component references, then computes
+    the transitive closure over the component dependency graph.
+    Returns names with ~ prefix.
+    """
+    # Direct refs from the page source
+    direct = {f"~{n}" for n in scan_components_from_sx(page_sx)}
+
+    # Transitive closure
+    all_needed: set[str] = set()
+    for name in direct:
+        all_needed.add(name)
+        val = env.get(name)
+        if isinstance(val, Component) and val.deps:
+            all_needed.update(val.deps)
+        else:
+            # deps not cached yet — compute on the fly
+            all_needed.update(transitive_deps(name, env))
+
+    return all_needed
diff --git a/shared/sx/helpers.py b/shared/sx/helpers.py
index c913ce7..88654e4 100644
--- a/shared/sx/helpers.py
+++ b/shared/sx/helpers.py
@@ -456,34 +456,39 @@ def sx_call(component_name: str, **kwargs: Any) -> str:
 
 
 
-def components_for_request() -> str:
+def components_for_request(source: str = "") -> str:
     """Return defcomp/defmacro source for definitions the client doesn't have yet.
 
     Reads the ``SX-Components`` header (comma-separated component names
     like ``~card,~nav-item``) and returns only the definitions the client
-    is missing.  If the header is absent, returns all defs.
+    is missing.  If *source* is provided, only sends components needed
+    for that source (plus transitive deps).  If the header is absent,
+    returns all needed defs.
     """
     from quart import request
-    from .jinja_bridge import client_components_tag, _COMPONENT_ENV
+    from .jinja_bridge import _COMPONENT_ENV
+    from .deps import components_needed
     from .types import Component, Macro
     from .parser import serialize
 
-    loaded_raw = request.headers.get("SX-Components", "")
-    if not loaded_raw:
-        # Client has nothing — send all
-        tag = client_components_tag()
-        if not tag:
-            return ""
-        start = tag.find(">") + 1
-        end = tag.rfind("</script>")
-        return tag[start:end] if start > 0 and end > start else ""
+    # Determine which components the page needs
+    if source:
+        needed = components_needed(source, _COMPONENT_ENV)
+    else:
+        needed = None  # all
+
+    loaded_raw = request.headers.get("SX-Components", "")
+    loaded = set(loaded_raw.split(",")) if loaded_raw else set()
 
-    loaded = set(loaded_raw.split(","))
     parts = []
     for key, val in _COMPONENT_ENV.items():
         if isinstance(val, Component):
+            comp_name = f"~{val.name}"
+            # Skip if not needed for this page
+            if needed is not None and comp_name not in needed and key not in needed:
+                continue
             # Skip components the client already has
-            if f"~{val.name}" in loaded or val.name in loaded:
+            if comp_name in loaded or val.name in loaded:
                 continue
             # Reconstruct defcomp source
             param_strs = ["&key"] + list(val.params)
@@ -530,7 +535,7 @@ def sx_response(source: str, status: int = 200,
     # For SX requests, prepend missing component definitions
     comp_defs = ""
     if request.headers.get("SX-Request"):
-        comp_defs = components_for_request()
+        comp_defs = components_for_request(source)
         if comp_defs:
             body = (f'<script type="text/sx" data-components>'
                     f'{comp_defs}</script>\n{body}')
@@ -641,11 +646,11 @@ 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, get_component_hash
-    from .css_registry import scan_classes_from_sx, lookup_rules, get_preamble, registry_loaded, store_css_hash
-    from .types import Component
+    from .jinja_bridge import components_for_page, css_classes_for_page
+    from .css_registry import lookup_rules, get_preamble, registry_loaded, store_css_hash
 
-    component_hash = get_component_hash()
+    # Per-page component bundle: only definitions this page needs
+    component_defs, component_hash = components_for_page(page_sx)
 
     # Check if client already has this version cached (via cookie)
     # In dev mode, always send full source so edits are visible immediately
@@ -653,28 +658,13 @@ def sx_page(ctx: dict, page_sx: str, *,
     if not _is_dev_mode() and 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
+    # Scan for CSS classes — only from components this page uses + page source
     sx_css = ""
     sx_css_classes = ""
     sx_css_hash = ""
     if registry_loaded():
-        # Union pre-computed component classes instead of re-scanning source
-        classes: set[str] = set()
-        for val in _COMPONENT_ENV.values():
-            if isinstance(val, Component) and val.css_classes:
-                classes.update(val.css_classes)
-        # Page sx is unique per request — scan it
-        classes.update(scan_classes_from_sx(page_sx))
+        classes = css_classes_for_page(page_sx)
         # Always include body classes
         classes.update(["bg-stone-50", "text-stone-900"])
         rules = lookup_rules(classes)
diff --git a/shared/sx/jinja_bridge.py b/shared/sx/jinja_bridge.py
index 50b9a94..1e01009 100644
--- a/shared/sx/jinja_bridge.py
+++ b/shared/sx/jinja_bridge.py
@@ -198,6 +198,10 @@ def register_components(sx_source: str) -> None:
                 all_classes = scan_classes_from_sx(sx_source)
             val.css_classes = set(all_classes)
 
+    # Recompute transitive deps for all components (cheap — just AST walking)
+    from .deps import compute_all_deps
+    compute_all_deps(_COMPONENT_ENV)
+
     _compute_component_hash()
 
 
@@ -322,6 +326,71 @@ def client_components_tag(*names: str) -> str:
     return f'<script type="text/sx" data-components>{source}</script>'
 
 
+def components_for_page(page_sx: str) -> tuple[str, str]:
+    """Return (component_defs_source, page_hash) for a page.
+
+    Scans *page_sx* for component references, computes the transitive
+    closure, and returns only the definitions needed for this page.
+    The hash is computed from the page-specific bundle for caching.
+    """
+    from .deps import components_needed
+    from .parser import serialize
+
+    needed = components_needed(page_sx, _COMPONENT_ENV)
+    if not needed:
+        return "", ""
+
+    # Also include macros — they're needed for client-side expansion
+    parts = []
+    for key, val in _COMPONENT_ENV.items():
+        if isinstance(val, Component):
+            if f"~{val.name}" in needed or key in needed:
+                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, pretty=True)
+                parts.append(f"(defcomp ~{val.name} {params_sx} {body_sx})")
+        elif isinstance(val, Macro):
+            # Include macros that are referenced in needed components' bodies
+            # For now, include all macros (they're small and often shared)
+            param_strs = list(val.params)
+            if val.rest_param:
+                param_strs.extend(["&rest", val.rest_param])
+            params_sx = "(" + " ".join(param_strs) + ")"
+            body_sx = serialize(val.body, pretty=True)
+            parts.append(f"(defmacro {val.name} {params_sx} {body_sx})")
+
+    if not parts:
+        return "", ""
+
+    source = "\n".join(parts)
+    digest = hashlib.sha256(source.encode()).hexdigest()[:12]
+    return source, digest
+
+
+def css_classes_for_page(page_sx: str) -> set[str]:
+    """Return CSS classes needed for a page's component bundle + page source.
+
+    Instead of unioning ALL component CSS classes, only includes classes
+    from components the page actually uses.
+    """
+    from .deps import components_needed
+    from .css_registry import scan_classes_from_sx
+
+    needed = components_needed(page_sx, _COMPONENT_ENV)
+    classes: set[str] = set()
+
+    for key, val in _COMPONENT_ENV.items():
+        if isinstance(val, Component):
+            if (f"~{val.name}" in needed or key in needed) and val.css_classes:
+                classes.update(val.css_classes)
+
+    # Page sx is unique per request — scan it
+    classes.update(scan_classes_from_sx(page_sx))
+    return classes
+
+
 def sx_css_all() -> str:
     """Return all CSS rules (preamble + utilities) for Jinja fallback pages."""
     from .css_registry import get_all_css
diff --git a/shared/sx/tests/test_deps.py b/shared/sx/tests/test_deps.py
new file mode 100644
index 0000000..8c88082
--- /dev/null
+++ b/shared/sx/tests/test_deps.py
@@ -0,0 +1,176 @@
+"""Tests for the component dependency analyzer."""
+
+import pytest
+from shared.sx.parser import parse_all
+from shared.sx.types import Component, Macro, Symbol
+from shared.sx.deps import (
+    _scan_ast,
+    transitive_deps,
+    compute_all_deps,
+    scan_components_from_sx,
+    components_needed,
+)
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def make_env(*sx_sources: str) -> dict:
+    """Parse and evaluate component definitions into an env dict."""
+    from shared.sx.evaluator import _eval, _trampoline
+    env: dict = {}
+    for source in sx_sources:
+        exprs = parse_all(source)
+        for expr in exprs:
+            _trampoline(_eval(expr, env))
+    return env
+
+
+# ---------------------------------------------------------------------------
+# _scan_ast
+# ---------------------------------------------------------------------------
+
+class TestScanAst:
+    def test_simple_component_ref(self):
+        env = make_env('(defcomp ~card (&key title) (div (~badge :label title)))')
+        comp = env["~card"]
+        refs = _scan_ast(comp.body)
+        assert refs == {"~badge"}
+
+    def test_no_refs(self):
+        env = make_env('(defcomp ~plain (&key text) (div :class "p-4" text))')
+        comp = env["~plain"]
+        refs = _scan_ast(comp.body)
+        assert refs == set()
+
+    def test_multiple_refs(self):
+        env = make_env(
+            '(defcomp ~page (&key title) (div (~header :title title) (~footer)))'
+        )
+        comp = env["~page"]
+        refs = _scan_ast(comp.body)
+        assert refs == {"~header", "~footer"}
+
+    def test_nested_in_control_flow(self):
+        env = make_env(
+            '(defcomp ~card (&key big) '
+            '  (if big (~big-card) (~small-card)))'
+        )
+        comp = env["~card"]
+        refs = _scan_ast(comp.body)
+        assert refs == {"~big-card", "~small-card"}
+
+    def test_refs_in_dict(self):
+        env = make_env(
+            '(defcomp ~wrap (&key) (div {:slot (~inner)}))'
+        )
+        comp = env["~wrap"]
+        refs = _scan_ast(comp.body)
+        assert refs == {"~inner"}
+
+
+# ---------------------------------------------------------------------------
+# transitive_deps
+# ---------------------------------------------------------------------------
+
+class TestTransitiveDeps:
+    def test_direct_dep(self):
+        env = make_env(
+            '(defcomp ~card (&key) (div (~badge)))',
+            '(defcomp ~badge (&key) (span "★"))',
+        )
+        deps = transitive_deps("~card", env)
+        assert deps == {"~badge"}
+
+    def test_transitive(self):
+        env = make_env(
+            '(defcomp ~page (&key) (div (~layout)))',
+            '(defcomp ~layout (&key) (div (~header) (~footer)))',
+            '(defcomp ~header (&key) (nav "header"))',
+            '(defcomp ~footer (&key) (footer "footer"))',
+        )
+        deps = transitive_deps("~page", env)
+        assert deps == {"~layout", "~header", "~footer"}
+
+    def test_circular(self):
+        """Circular deps should not cause infinite recursion."""
+        env = make_env(
+            '(defcomp ~a (&key) (div (~b)))',
+            '(defcomp ~b (&key) (div (~a)))',
+        )
+        deps = transitive_deps("~a", env)
+        assert deps == {"~b"}
+
+    def test_no_deps(self):
+        env = make_env('(defcomp ~leaf (&key) (span "hi"))')
+        deps = transitive_deps("~leaf", env)
+        assert deps == set()
+
+    def test_missing_component(self):
+        """Referencing a component not in env should not crash."""
+        env = make_env('(defcomp ~card (&key) (div (~unknown)))')
+        deps = transitive_deps("~card", env)
+        assert "~unknown" in deps
+
+    def test_without_tilde_prefix(self):
+        env = make_env(
+            '(defcomp ~card (&key) (div (~badge)))',
+            '(defcomp ~badge (&key) (span "★"))',
+        )
+        deps = transitive_deps("card", env)
+        assert deps == {"~badge"}
+
+
+# ---------------------------------------------------------------------------
+# compute_all_deps
+# ---------------------------------------------------------------------------
+
+class TestComputeAllDeps:
+    def test_sets_deps_on_components(self):
+        env = make_env(
+            '(defcomp ~page (&key) (div (~card)))',
+            '(defcomp ~card (&key) (div (~badge)))',
+            '(defcomp ~badge (&key) (span "★"))',
+        )
+        compute_all_deps(env)
+        assert env["~page"].deps == {"~card", "~badge"}
+        assert env["~card"].deps == {"~badge"}
+        assert env["~badge"].deps == set()
+
+
+# ---------------------------------------------------------------------------
+# scan_components_from_sx
+# ---------------------------------------------------------------------------
+
+class TestScanComponentsFromSx:
+    def test_basic(self):
+        source = '(~card :title "hi" (~badge :label "new"))'
+        refs = scan_components_from_sx(source)
+        assert refs == {"card", "badge"}
+
+    def test_no_components(self):
+        source = '(div :class "p-4" (p "hello"))'
+        refs = scan_components_from_sx(source)
+        assert refs == set()
+
+
+# ---------------------------------------------------------------------------
+# components_needed
+# ---------------------------------------------------------------------------
+
+class TestComponentsNeeded:
+    def test_page_with_deps(self):
+        env = make_env(
+            '(defcomp ~page-layout (&key) (div (~nav) (~footer)))',
+            '(defcomp ~nav (&key) (nav "nav"))',
+            '(defcomp ~footer (&key) (footer "footer"))',
+            '(defcomp ~unused (&key) (div "not needed"))',
+        )
+        compute_all_deps(env)
+        page_sx = '(~page-layout)'
+        needed = components_needed(page_sx, env)
+        assert "~page-layout" in needed
+        assert "~nav" in needed
+        assert "~footer" in needed
+        assert "~unused" not in needed
diff --git a/shared/sx/types.py b/shared/sx/types.py
index 044c383..4207421 100644
--- a/shared/sx/types.py
+++ b/shared/sx/types.py
@@ -167,6 +167,7 @@ class Component:
     body: Any                 # unevaluated s-expression body
     closure: dict[str, Any] = field(default_factory=dict)
     css_classes: set[str] = field(default_factory=set)  # pre-scanned :class values
+    deps: set[str] = field(default_factory=set)        # transitive component deps (~names)
 
     def __repr__(self):
         return f"<Component ~{self.name}({', '.join(self.params)})>"