diff --git a/web/src/Registry.tsx b/web/src/Registry.tsx
index 0d288f9..3ac90c2 100644
--- a/web/src/Registry.tsx
+++ b/web/src/Registry.tsx
@@ -5,6 +5,7 @@ import {
   GitMerge,
   Trash2,
   FolderTree,
+  FolderPlus,
   Tag as TagIcon,
   Store,
   CandlestickChart,
@@ -32,6 +33,10 @@ import {
 import type { Mutate } from "./ui";
 type Entity = "category" | "tag" | "merchant" | "instrument";
 type Item = Category | Tag | Merchant | Instrument;
+const protectedCategoryIDs = new Set([
+  "cat_expenses_unclassified",
+  "cat_income_unclassified",
+]);
 const titles = {
   category: "Categories",
   tag: "Tags",
@@ -82,83 +87,105 @@ export function Registry({
             ? { id: "", isin: "", name: "", currency: "EUR", symbol: "" }
             : { id: "", name: "" },
     );
-  const row = (item: Item, depth = 0) => (
-    <div className="registry-row" key={item.id}>
-      <div
-        className="registry-label"
-        style={{ paddingLeft: `${depth * 23}px` }}
-      >
-        {entity === "category" ? (
-          <FolderTree size={18} />
-        ) : entity === "tag" ? (
-          <TagIcon size={18} />
-        ) : entity === "instrument" ? (
-          <CandlestickChart size={18} />
-        ) : (
-          <Store size={18} />
-        )}
-        <div>
-          <strong>{item.name}</strong>
-          {"kind" in item && (
-            <small>
-              {item.kind}
-              {!item.parent_id ? " root" : ""}
-            </small>
-          )}
-          {"aliases" in item && (
-            <small>
-              {item.aliases.length ? item.aliases.join(" · ") : "No aliases"}
-              {item.use_defaults ? " · Defaults enabled" : ""}
-            </small>
-          )}
-          {"hint" in item && item.hint && <small>{item.hint}</small>}
-          {"isin" in item && (
-            <small>
-              {item.isin} · {item.currency} ·{" "}
-              {item.symbol
-                ? item.quote
-                  ? `${item.symbol} at ${item.quote} on ${item.quoted_at}`
-                  : `${item.symbol}, not yet quoted`
-                : "No market symbol, so unpriced"}
-            </small>
-          )}
-        </div>
-      </div>
-      {"default_category_id" in item && item.default_category_id && (
-        <span className="muted registry-detail">
-          {categoryPath(data, item.default_category_id)}
-        </span>
-      )}
-      <div className="row-actions">
-        <button
-          className="icon-button"
-          title={`Edit ${item.name}`}
-          aria-label={`Edit ${item.name}`}
-          onClick={() => setEditing(item)}
+  const createChild = (parent: Category) =>
+    setEditing({
+      id: "",
+      name: "",
+      parent_id: parent.id,
+      kind: parent.kind,
+      hint: "",
+    });
+  const row = (item: Item, depth = 0) => {
+    const category = entity === "category" && "kind" in item ? item : null;
+    return (
+      <div className="registry-row" key={item.id}>
+        <div
+          className="registry-label"
+          style={{ paddingLeft: `${depth * 23}px` }}
         >
-          <Pencil size={16} />
-        </button>
-        {entity !== "instrument" && (
+          {entity === "category" ? (
+            <FolderTree size={18} />
+          ) : entity === "tag" ? (
+            <TagIcon size={18} />
+          ) : entity === "instrument" ? (
+            <CandlestickChart size={18} />
+          ) : (
+            <Store size={18} />
+          )}
+          <div>
+            <strong>{item.name}</strong>
+            {"kind" in item && (
+              <small>
+                {item.kind}
+                {!item.parent_id ? " root" : ""}
+              </small>
+            )}
+            {"aliases" in item && (
+              <small>
+                {item.aliases.length ? item.aliases.join(" · ") : "No aliases"}
+                {item.use_defaults ? " · Defaults enabled" : ""}
+              </small>
+            )}
+            {"hint" in item && item.hint && <small>{item.hint}</small>}
+            {"isin" in item && (
+              <small>
+                {item.isin} · {item.currency} ·{" "}
+                {item.symbol
+                  ? item.quote
+                    ? `${item.symbol} at ${item.quote} on ${item.quoted_at}`
+                    : `${item.symbol}, not yet quoted`
+                  : "No market symbol, so unpriced"}
+              </small>
+            )}
+          </div>
+        </div>
+        {"default_category_id" in item && item.default_category_id && (
+          <span className="muted registry-detail">
+            {categoryPath(data, item.default_category_id)}
+          </span>
+        )}
+        <div className="row-actions">
+          {category && !protectedCategoryIDs.has(category.id) && (
+            <button
+              className="button subtle category-child-action"
+              title={`Add a child category under ${category.name}`}
+              aria-label={`Add a child category under ${category.name}`}
+              onClick={() => createChild(category)}
+            >
+              <FolderPlus size={15} />
+              Add child
+            </button>
+          )}
           <button
             className="icon-button"
-            title={`Merge ${item.name}`}
-            aria-label={`Merge ${item.name}`}
-            onClick={() => setAction({ item, action: "merge" })}
+            title={`Edit ${item.name}`}
+            aria-label={`Edit ${item.name}`}
+            onClick={() => setEditing(item)}
           >
-            <GitMerge size={16} />
+            <Pencil size={16} />
           </button>
-        )}
-        <button
-          className="icon-button danger"
-          title={`Delete ${item.name}`}
-          aria-label={`Delete ${item.name}`}
-          onClick={() => setAction({ item, action: "delete" })}
-        >
-          <Trash2 size={16} />
-        </button>
+          {entity !== "instrument" && (
+            <button
+              className="icon-button"
+              title={`Merge ${item.name}`}
+              aria-label={`Merge ${item.name}`}
+              onClick={() => setAction({ item, action: "merge" })}
+            >
+              <GitMerge size={16} />
+            </button>
+          )}
+          <button
+            className="icon-button danger"
+            title={`Delete ${item.name}`}
+            aria-label={`Delete ${item.name}`}
+            onClick={() => setAction({ item, action: "delete" })}
+          >
+            <Trash2 size={16} />
+          </button>
+        </div>
       </div>
-    </div>
-  );
+    );
+  };
   const tree = (
     parent: string | undefined,
     depth = 0,
@@ -181,7 +208,7 @@ export function Registry({
           <h2>{titles[entity]}</h2>
           <p>
             {entity === "category"
-              ? "A clear home for every transaction. Parent categories roll up their children."
+              ? "Organize spending and income into a tree. Use Add child on any category to create a nested category."
               : entity === "tag"
                 ? "Flexible labels that work across your accounts and categories."
                 : entity === "instrument"
@@ -549,15 +576,18 @@ function RegistryEditor({
                   <option value="income">Income</option>
                 </select>
               </Field>
-              <Field label="Parent category">
+              <Field
+                label="Parent category"
+                hint="Choose an existing category to nest this one. Use Add child on the category list when you want to add a nested category."
+              >
                 <CategoryCombobox
                   data={data}
                   kind={kind}
                   exclude={[...descendants]}
-                  emptyLabel="No parent (root)"
-                  mutate={mutate}
+                  emptyLabel="No parent (top level)"
                   value={parent}
                   onChange={setParent}
+                  placeholder="Choose a parent category"
                 />
               </Field>
               <p className="muted">
diff --git a/web/src/Transactions.tsx b/web/src/Transactions.tsx
index 612ce9b..5b0e5f6 100644
--- a/web/src/Transactions.tsx
+++ b/web/src/Transactions.tsx
@@ -496,13 +496,17 @@ function TransactionEditor({
             )}
           </div>
           {value.kind !== "transfer" && value.kind !== "investment" && (
-            <Field label="Category">
+            <Field
+              label="Category"
+              hint="Choose a leaf category. To add one now, type a new name and choose “Create category”. Use “Parent / Child” to nest it under an existing category."
+            >
               <CategoryCombobox
                 data={data}
                 kind={value.kind}
                 leavesOnly
                 required
                 mutate={mutate}
+                placeholder="Select or type to add a category"
                 value={value.category_id || ""}
                 onChange={(category_id) =>
                   setValue((v) => ({ ...v, category_id }))
diff --git a/web/src/styles.css b/web/src/styles.css
index d704a17..ef3ff4a 100644
--- a/web/src/styles.css
+++ b/web/src/styles.css
@@ -903,6 +903,11 @@ tbody tr:hover {
   gap: 5px;
   align-items: center;
 }
+.category-child-action {
+  min-height: 32px;
+  padding: 6px 9px;
+  font-size: 11px;
+}
 .modal {
   border: 1px solid #dce5eb;
   border-radius: 12px;
diff --git a/web/src/ui.tsx b/web/src/ui.tsx
index 9e02156..0edde76 100644
--- a/web/src/ui.tsx
+++ b/web/src/ui.tsx
@@ -730,9 +730,9 @@ export function CategoryOptions({
 }
 // CategoryCombobox is the one category picker: options are full paths, and
 // with a mutate handle an unmatched name can be created in place. A bare name
-// lands under the kind's root; "Parent / Name" creates under that parent.
-// leavesOnly matches the server rule that assigned categories must be leaves;
-// a freshly created category is always a leaf.
+// is offered under each matching root; "Parent / Name" creates under that
+// existing parent. leavesOnly matches the server rule that assigned categories
+// must be leaves; a freshly created category is always a leaf.
 export function CategoryCombobox({
   data,
   value,
@@ -782,7 +782,7 @@ export function CategoryCombobox({
     const name = segments[segments.length - 1];
     const row = (parent: Category): ComboCreate => ({
       key: parent.id,
-      label: `Create "${name}" in ${categoryPath(data, parent.id)}`,
+      label: `Create category "${name}" in ${categoryPath(data, parent.id)}`,
       run: async () =>
         onChange(
           await createCategory(mutate, data, {
@@ -813,7 +813,7 @@ export function CategoryCombobox({
       placeholder={placeholder}
       emptyText={
         mutate
-          ? "No matching category. Type a name to create it."
+          ? "No match. Type a category name and choose Create category."
           : "No matching category."
       }
       create={create}