diff --git a/README.md b/README.md
index 8beaffa..88c8626 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,7 @@ WinterCMS theme components such as `journalPost` and `journalPosts` are a later
 ## Features
 
 - **Posts.** `models.Post` maps `golem15_journal_posts`. Translatable fields are title, content, content_html, excerpt, metadata, and slug (indexed). Fillable does not include `redactor_id`, `content_html`, or `user_id`. Attachments `featured_images` and `content_images` use `system_files` under the same MorphName. YAML admin uses `mltext`/`mlmarkdown`. `classes.FormatHTML` regenerates `content_html` on admin save.
-- **Categories and tags.** `models.Category` is translatable (name, description, slug). Fillable is name, slug, code, description, parent_id; nest_* columns exist in DDL and are not fillable. `models.Tag` is not translatable. Fillable is name, slug, description. Pivots are `golem15_journal_posts_categories` and `golem15_journal_posts_tags`.
+- **Categories and tags.** `models.Category` is translatable (name, description, slug). It also stores `content`, an HTML host column that is not translatable, edited in the admin as a textarea. Fillable is name, slug, code, description, content and parent_id; nest_* columns exist in DDL and are not fillable. `models.Tag` is not translatable. Fillable is name, slug, description. Pivots are `golem15_journal_posts_categories` and `golem15_journal_posts_tags`.
 - **Settings.** Singleton row ID=1 on `golem15_journal_settings`, not PHP `system_settings`. `search_use_typesense` defaults to false. A fresh save never contacts Typesense.
 - **Public HTTP.** Anonymous GET `/_journal/api/v1/posts`, `/posts/{slug}`, `/categories`, `/tags`, `/rss`, `/authors/{author}`, and `/authors/{author}/posts`. Writes under the same prefix require a cabana backend JWT (`aud=backend`).
 - **Author slug.** Plugin migration adds `backend_users.golem15_bloghub_author_slug`. The column stores the public author slug that the author routes resolve.
@@ -86,6 +86,8 @@ GET /_journal/api/v1/authors/jane-doe/posts?page=2
 
 `content` is the category's HTML body for a category landing page. It is stored and returned as is: it is not markdown and the API does not render, trim or sanitize it. It is `null` when unset, and it is the same in every locale, because it is a host column and not translatable. A consumer that renders it as HTML must apply its own gate or sanitizer first.
 
+The admin Categories form refuses content that fails `classes.CheckHTML` with a `422` on `content`, and stores blank content as `null`. Rows written by SQL or by import commands bypass that gate, so consumers keep their own gate.
+
 ```json
 {"data":[{"id":4,"name":"Acme news","slug":"news","description":null,"content":"<h2>Acme news</h2><p>Pillar copy</p>","parent_id":null,"nest_depth":0,"post_count":3}]}
 ```
@@ -169,12 +171,13 @@ func (Post) MorphName() string             { return `Golem15\Journal\Models\Post
 | `models.Post.CanEdit` | Owner or `golem15.journal.access_other_posts`. |
 | `models.Category` | Category row; `TableName` is `golem15_journal_categories`; `Content` holds the HTML body served as `content`. |
 | `models.Category.MorphName` | PHP class string `Golem15\Journal\Models\Category`. |
-| `models.Category.Fillable` | `name`, `slug`, `code`, `description`, `parent_id`. |
+| `models.Category.Fillable` | `name`, `slug`, `code`, `description`, `content`, `parent_id`. |
 | `models.Tag` | Tag row; `TableName` is `golem15_journal_tags`. |
 | `models.Tag.Fillable` | `name`, `slug`, `description`. |
 | `models.Settings` | Singleton settings row; `TableName` is `golem15_journal_settings`. |
 | `models.All` | Models registered by this plugin. |
 | `updates.All` | gormigrate steps registered by this plugin. |
+| `classes.CheckHTML` | The `FormatHTML` safety gate for HTML stored as is, such as category content. |
 
 ## CLI commands
 
diff --git a/classes/check_html_test.go b/classes/check_html_test.go
new file mode 100644
index 0000000..cc6f2fd
--- /dev/null
+++ b/classes/check_html_test.go
@@ -0,0 +1,34 @@
+package classes
+
+import "testing"
+
+func TestCheckHTML(t *testing.T) {
+	cases := []struct {
+		name string
+		in   string
+		ok   bool
+	}{
+		{"empty", "", true},
+		{"heading and link", `<h2>Cordyceps</h2><p>Plain <a href="https://example.test/a">link</a></p>`, true},
+		{"table", `<table><thead><tr><th>A</th></tr></thead><tbody><tr><td>1</td></tr></tbody></table>`, true},
+		{"script", `<script>alert(1)</script>`, false},
+		{"iframe", `<iframe src="https://example.test/"></iframe>`, false},
+		{"object", `<object data=x>`, false},
+		{"embed", `<embed src=x>`, false},
+		{"event handler", `<img src=x onerror="alert(1)">`, false},
+		{"javascript url", `<a href="javascript:alert(1)">`, false},
+		{"vbscript url mixed case", `<a href="VBScript:x">`, false},
+		{"data url", `<img src="data:image/png;base64,AAAA">`, false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := CheckHTML(tc.in)
+			if tc.ok && err != nil {
+				t.Fatalf("CheckHTML(%q) = %v, want nil", tc.in, err)
+			}
+			if !tc.ok && err == nil {
+				t.Fatalf("CheckHTML(%q) = nil, want an error", tc.in)
+			}
+		})
+	}
+}
diff --git a/classes/format_html.go b/classes/format_html.go
index 58c3274..e6588db 100644
--- a/classes/format_html.go
+++ b/classes/format_html.go
@@ -37,6 +37,13 @@ func FormatHTML(src string) (string, error) {
 	return html, nil
 }
 
+// CheckHTML applies the FormatHTML safety gate to HTML that is stored as is,
+// such as category content. It refuses raw script, iframe, object and embed
+// tags, event handler attributes and javascript, vbscript or data URL schemes.
+func CheckHTML(html string) error {
+	return rejectUnsafe(html)
+}
+
 func rejectUnsafe(html string) error {
 	if markdownUnsafeTag.MatchString(html) {
 		return fmt.Errorf("journal: rendered HTML contains raw unsafe tags")
diff --git a/controllers/categories.go b/controllers/categories.go
index caaa237..794ae1a 100644
--- a/controllers/categories.go
+++ b/controllers/categories.go
@@ -1,6 +1,11 @@
 package controllers
 
 import (
+	"context"
+	"errors"
+	"strings"
+
+	"git.golem15.com/golem15/sm-journal-plugin/classes"
 	"git.golem15.com/golem15/sm-journal-plugin/models"
 	"git.golem15.com/golem15/summercms/modules/backpack"
 	"git.golem15.com/golem15/summercms/modules/cabana"
@@ -40,9 +45,46 @@ func (categoriesAdminController) AdminFieldRelations() []cabana.FieldRelationCon
 	}}
 }
 
+func (categoriesAdminController) FormBeforeCreate(ctx context.Context, model any) error {
+	cat, ok := model.(*models.Category)
+	if !ok || cat == nil {
+		return errors.New("categories admin: form model is not a category")
+	}
+	return prepareCategoryWrite(cat)
+}
+
+func (categoriesAdminController) FormBeforeUpdate(ctx context.Context, model any) error {
+	cat, ok := model.(*models.Category)
+	if !ok || cat == nil {
+		return errors.New("categories admin: form model is not a category")
+	}
+	return prepareCategoryWrite(cat)
+}
+
+// prepareCategoryWrite gates the category HTML body (D-21): blank content is
+// stored as NULL, and content that fails classes.CheckHTML is a 422 on
+// content. Any other content is stored exactly as submitted.
+func prepareCategoryWrite(cat *models.Category) error {
+	if cat.Content == nil {
+		return nil
+	}
+	if strings.TrimSpace(*cat.Content) == "" {
+		cat.Content = nil
+		return nil
+	}
+	if err := classes.CheckHTML(*cat.Content); err != nil {
+		return &cabana.ValidationError{Details: map[string]any{
+			"content": []string{err.Error()},
+		}}
+	}
+	return nil
+}
+
 var (
 	_ pact.AdminController         = categoriesAdminController{}
 	_ pact.AdminPermissioned       = categoriesAdminController{}
 	_ pact.AdminRecordSource       = categoriesAdminController{}
+	_ pact.FormBeforeCreate        = categoriesAdminController{}
+	_ pact.FormBeforeUpdate        = categoriesAdminController{}
 	_ cabana.FieldRelationProvider = categoriesAdminController{}
 )
diff --git a/journal_api_categories_test.go b/journal_api_categories_test.go
index b096198..3e81e95 100644
--- a/journal_api_categories_test.go
+++ b/journal_api_categories_test.go
@@ -3,11 +3,14 @@ package journal_test
 import (
 	"encoding/json"
 	"net/http"
+	"net/http/httptest"
 	"reflect"
 	"sort"
+	"strconv"
 	"testing"
 	"time"
 
+	"git.golem15.com/golem15/sm-journal-plugin/controllers"
 	"git.golem15.com/golem15/sm-journal-plugin/models"
 )
 
@@ -129,3 +132,145 @@ func TestJournalCategoryContentAPI(t *testing.T) {
 		t.Fatalf("post listed-content missing from /posts: %s", rec.Body.String())
 	}
 }
+
+const adminCategoriesPath = "/golem15/journal/categories"
+
+func TestCategoriesAdminContent(t *testing.T) {
+	env := newPostsEnv(t)
+	token := env.admin(t, controllers.PermissionAccessCategories)
+
+	schema := adminDecode(t, env.expect(t, http.StatusOK, http.MethodGet, adminAPI(adminCategoriesPath+"/schema/form"), token, nil))
+	var form struct {
+		Fields []struct {
+			Name string `json:"name"`
+			Type string `json:"type"`
+			Size string `json:"size"`
+		} `json:"fields"`
+	}
+	if err := json.Unmarshal(schema.Data, &form); err != nil {
+		t.Fatalf("form schema %s: %v", schema.Data, err)
+	}
+	contentAt := -1
+	for i, f := range form.Fields {
+		if f.Name != "content" {
+			continue
+		}
+		contentAt = i
+		if f.Type != "textarea" || f.Size != "huge" {
+			t.Fatalf("content field = %+v, want textarea size huge", f)
+		}
+	}
+	if contentAt < 1 || form.Fields[contentAt-1].Name != "description" {
+		t.Fatalf("content field must follow description: %s", schema.Data)
+	}
+
+	safe := "<h2>Acme</h2>\n<p>Pillar <a href=\"https://example.test/a\">copy</a></p>"
+	name := map[string]any{"en": "Acme news", "pl": "Wiadomości Acme"}
+	slug := map[string]any{"en": "acme-news", "pl": "wiadomosci-acme"}
+	rec := env.expect(t, http.StatusCreated, http.MethodPost, adminAPI(adminCategoriesPath), token, map[string]any{
+		"name":    name,
+		"slug":    slug,
+		"content": safe,
+	})
+	var created struct {
+		ID uint `json:"id"`
+	}
+	if err := json.Unmarshal(adminDecode(t, rec).Data, &created); err != nil || created.ID == 0 {
+		t.Fatalf("create data %s: %v", rec.Body.String(), err)
+	}
+	storedContent := func(t *testing.T) *string {
+		t.Helper()
+		var cat models.Category
+		if err := env.gdb.First(&cat, created.ID).Error; err != nil {
+			t.Fatal(err)
+		}
+		return cat.Content
+	}
+	if got := storedContent(t); got == nil || *got != safe {
+		t.Fatalf("stored content = %#v, want %q", got, safe)
+	}
+	rows := categoryRowsBySlug(t, env, "/_journal/api/v1/categories?include_empty=1")
+	if got, ok := rows["acme-news"]["content"].(string); !ok || got != safe {
+		t.Fatalf("API content = %#v, want %q", rows["acme-news"]["content"], safe)
+	}
+
+	assertContentRefused := func(t *testing.T, rec *httptest.ResponseRecorder) {
+		t.Helper()
+		if rec.Code != http.StatusUnprocessableEntity {
+			t.Fatalf("status = %d, want 422: %s", rec.Code, rec.Body.String())
+		}
+		var body struct {
+			Error struct {
+				Code    string         `json:"code"`
+				Details map[string]any `json:"details"`
+			} `json:"error"`
+		}
+		if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+			t.Fatalf("422 body %s: %v", rec.Body.String(), err)
+		}
+		if body.Error.Code != "validation_failed" {
+			t.Fatalf("error code = %q, want validation_failed", body.Error.Code)
+		}
+		if _, ok := body.Error.Details["content"]; !ok {
+			t.Fatalf("details do not name content: %s", rec.Body.String())
+		}
+	}
+
+	t.Run("unsafe create refused", func(t *testing.T) {
+		rec := env.call(t, http.MethodPost, adminAPI(adminCategoriesPath), token, map[string]any{
+			"name":    map[string]any{"en": "Unsafe", "pl": "Niebezpieczna"},
+			"slug":    map[string]any{"en": "unsafe-acme", "pl": "niebezpieczna-acme"},
+			"content": "<p onclick=\"steal()\">x</p>",
+		})
+		assertContentRefused(t, rec)
+		var n int64
+		if err := env.gdb.Model(&models.Category{}).Where("slug = ?", "unsafe-acme").Count(&n).Error; err != nil {
+			t.Fatal(err)
+		}
+		if n != 0 {
+			t.Fatalf("unsafe-acme rows = %d, want 0", n)
+		}
+	})
+
+	itemPath := adminAPI(adminCategoriesPath + "/" + strconv.FormatUint(uint64(created.ID), 10))
+
+	t.Run("unsafe update refused", func(t *testing.T) {
+		rec := env.call(t, http.MethodPut, itemPath, token, map[string]any{
+			"name":    name,
+			"slug":    slug,
+			"content": "<a href=\"javascript:alert(1)\">x</a>",
+		})
+		assertContentRefused(t, rec)
+		if got := storedContent(t); got == nil || *got != safe {
+			t.Fatalf("stored content after refused update = %#v, want %q", got, safe)
+		}
+	})
+
+	t.Run("blank update stores null", func(t *testing.T) {
+		rec := env.call(t, http.MethodPut, itemPath, token, map[string]any{
+			"name":    name,
+			"slug":    slug,
+			"content": "   ",
+		})
+		if rec.Code < 200 || rec.Code > 299 {
+			t.Fatalf("blank update = %d, want 2xx: %s", rec.Code, rec.Body.String())
+		}
+		if got := storedContent(t); got != nil {
+			t.Fatalf("stored content = %q, want NULL", *got)
+		}
+		rows := categoryRowsBySlug(t, env, "/_journal/api/v1/categories?include_empty=1")
+		assertNullContent(t, rows, "acme-news")
+	})
+
+	t.Run("posts-only token forbidden", func(t *testing.T) {
+		postsOnly := env.admin(t, controllers.PermissionAccessPosts)
+		rec := env.call(t, http.MethodPost, adminAPI(adminCategoriesPath), postsOnly, map[string]any{
+			"name":    map[string]any{"en": "Denied", "pl": "Odmowa"},
+			"slug":    map[string]any{"en": "denied-acme", "pl": "odmowa-acme"},
+			"content": safe,
+		})
+		if rec.Code != http.StatusForbidden {
+			t.Fatalf("posts-only create = %d, want 403: %s", rec.Code, rec.Body.String())
+		}
+	})
+}
diff --git a/lang/en/lang.yaml b/lang/en/lang.yaml
index 4be9e74..8bd9aef 100644
--- a/lang/en/lang.yaml
+++ b/lang/en/lang.yaml
@@ -110,6 +110,8 @@ category:
   name: Name
   name_placeholder: New category name
   description: Description
+  content: "Content"
+  content_comment: "HTML shown on the category page above its post list. Unsafe HTML (scripts, frames, event handlers, javascript, vbscript and data URLs) is refused."
   slug: Slug
   slug_placeholder: new-category-slug
   posts: Posts
diff --git a/lang/pl/lang.yaml b/lang/pl/lang.yaml
index 3868e65..dbdad7b 100644
--- a/lang/pl/lang.yaml
+++ b/lang/pl/lang.yaml
@@ -74,6 +74,8 @@ category:
   name: Nazwa
   name_placeholder: Nazwa nowej kategorii
   description: Opis
+  content: "Treść"
+  content_comment: "Kod HTML wyświetlany na stronie kategorii nad listą wpisów. Niebezpieczny HTML (skrypty, ramki, atrybuty zdarzeń, adresy javascript, vbscript i data) jest odrzucany."
   slug: Alias
   slug_placeholder: alias-nowej-kategorii
   posts: Posty
diff --git a/models/category.go b/models/category.go
index 0dc3659..a6d427e 100644
--- a/models/category.go
+++ b/models/category.go
@@ -29,7 +29,7 @@ func (Category) TranslatableIndexes() []string { return []string{"slug"} }
 
 // Fillable is JOURNAL-002: nest_* stay out of mass assignment.
 func (Category) Fillable() []string {
-	return []string{"name", "slug", "code", "description", "parent_id"}
+	return []string{"name", "slug", "code", "description", "content", "parent_id"}
 }
 
 func (Category) Rules() map[string]string {
diff --git a/models/category/fields.yaml b/models/category/fields.yaml
index bd57cb3..05f90c3 100644
--- a/models/category/fields.yaml
+++ b/models/category/fields.yaml
@@ -22,3 +22,9 @@ fields:
         type: mltextarea
         size: large
         span: full
+    content:
+        label: golem15.journal::lang.category.content
+        comment: golem15.journal::lang.category.content_comment
+        type: textarea
+        size: huge
+        span: full
diff --git a/models/fillable_test.go b/models/fillable_test.go
index 22c1603..7d98d16 100644
--- a/models/fillable_test.go
+++ b/models/fillable_test.go
@@ -39,7 +39,7 @@ func TestFillable(t *testing.T) {
 	})
 
 	t.Run("category_excludes_nest", func(t *testing.T) {
-		if got := (models.Category{}).Fillable(); !reflect.DeepEqual(got, []string{"name", "slug", "code", "description", "parent_id"}) {
+		if got := (models.Category{}).Fillable(); !reflect.DeepEqual(got, []string{"name", "slug", "code", "description", "content", "parent_id"}) {
 			t.Fatalf("Category.Fillable = %#v", got)
 		}
 		left := 3
@@ -48,6 +48,7 @@ func TestFillable(t *testing.T) {
 			"name":       "Essays",
 			"slug":       "essays",
 			"code":       "ess",
+			"content":    "<p>Essay hub</p>",
 			"nest_left":  9,
 			"nest_right": 10,
 			"nest_depth": 2,
@@ -58,6 +59,9 @@ func TestFillable(t *testing.T) {
 		if cat.Name != "Essays" || cat.Slug != "essays" {
 			t.Fatalf("category fill = %+v", cat)
 		}
+		if cat.Content == nil || *cat.Content != "<p>Essay hub</p>" {
+			t.Fatalf("category content fill = %#v", cat.Content)
+		}
 		if cat.ID != 0 {
 			t.Fatalf("id was mass-assigned: %d", cat.ID)
 		}