diff --git a/internal/gitea/client.go b/internal/gitea/client.go
index 105165d..9915bb9 100644
--- a/internal/gitea/client.go
+++ b/internal/gitea/client.go
@@ -708,15 +708,20 @@ func (c *Client) SubmitReview(ctx context.Context, token, owner, repo string, in
 
 // CloseIssue closes an issue by setting its state to "closed".
 func (c *Client) CloseIssue(ctx context.Context, token, owner, repo string, index int64) error {
-	payload, err := json.Marshal(map[string]string{"state": "closed"})
+	return c.SetIssueState(ctx, token, owner, repo, index, "closed")
+}
+
+// SetIssueState sets an issue's state (e.g. "open" or "closed").
+func (c *Client) SetIssueState(ctx context.Context, token, owner, repo string, index int64, state string) error {
+	payload, err := json.Marshal(map[string]string{"state": state})
 	if err != nil {
-		return fmt.Errorf("marshaling close request: %w", err)
+		return fmt.Errorf("marshaling state change: %w", err)
 	}
 
 	path := fmt.Sprintf("/repos/%s/%s/issues/%d", owner, repo, index)
 	resp, err := c.doRequest(ctx, token, http.MethodPatch, path, strings.NewReader(string(payload)))
 	if err != nil {
-		return fmt.Errorf("closing issue: %w", err)
+		return fmt.Errorf("setting issue state: %w", err)
 	}
 	resp.Body.Close()
 
@@ -724,6 +729,11 @@ func (c *Client) CloseIssue(ctx context.Context, token, owner, repo string, inde
 	return nil
 }
 
+// AddComment creates a comment on an issue and returns the created Comment.
+func (c *Client) AddComment(ctx context.Context, token, owner, repo string, index int64, body string) (*Comment, error) {
+	return c.PostComment(ctx, token, owner, repo, index, body)
+}
+
 // PostComment creates a comment on an issue and returns the created Comment.
 func (c *Client) PostComment(ctx context.Context, token, owner, repo string, index int64, body string) (*Comment, error) {
 	payload, err := json.Marshal(map[string]string{"body": body})
diff --git a/internal/gitea/client_test.go b/internal/gitea/client_test.go
index e261cc1..5c839ed 100644
--- a/internal/gitea/client_test.go
+++ b/internal/gitea/client_test.go
@@ -241,6 +241,76 @@ func TestCloseIssue(t *testing.T) {
 	}
 }
 
+func TestSetIssueState(t *testing.T) {
+	tests := []struct {
+		name  string
+		state string
+	}{
+		{"close", "closed"},
+		{"reopen", "open"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				if r.Method != http.MethodPatch {
+					t.Errorf("expected PATCH, got %s", r.Method)
+				}
+				if r.URL.Path != "/api/v1/repos/owner1/repo1/issues/42" {
+					t.Errorf("unexpected path: %s", r.URL.Path)
+				}
+
+				var body map[string]string
+				if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+					t.Fatalf("failed to decode body: %v", err)
+				}
+				if body["state"] != tt.state {
+					t.Errorf("expected state=%q, got %q", tt.state, body["state"])
+				}
+
+				w.WriteHeader(http.StatusOK)
+				json.NewEncoder(w).Encode(map[string]string{"state": tt.state})
+			}))
+			defer server.Close()
+
+			c := NewClient(server.URL)
+			c.setCache("issues-org1", "should-be-invalidated")
+
+			err := c.SetIssueState(context.Background(), "test-token", "owner1", "repo1", 42, tt.state)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+
+			_, ok := c.getFromCache("issues-org1")
+			if ok {
+				t.Error("expected cache to be invalidated after SetIssueState")
+			}
+		})
+	}
+}
+
+func TestAddComment(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		comment := map[string]interface{}{
+			"id":         1,
+			"body":       "test",
+			"user":       map[string]string{"login": "testuser"},
+			"created_at": "2026-03-26T12:00:00Z",
+		}
+		json.NewEncoder(w).Encode(comment)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	comment, err := c.AddComment(context.Background(), "test-token", "owner1", "repo1", 42, "test")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if comment.Body != "test" {
+		t.Errorf("comment.Body = %q, want %q", comment.Body, "test")
+	}
+}
+
 func TestPostComment(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != http.MethodPost {
diff --git a/internal/handlers/handlers.go b/internal/handlers/handlers.go
index 364df0f..2207ecf 100644
--- a/internal/handlers/handlers.go
+++ b/internal/handlers/handlers.go
@@ -42,6 +42,8 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("POST /issues", h.CreateIssue)
 	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/labels", h.ApplyLabels)
 	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/close", h.CloseIssue)
+	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/state", h.SetIssueState)
+	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/comments", h.AddComment)
 	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/comment", h.AddComment)
 
 	// Issue detail.
@@ -630,6 +632,53 @@ func (h *Handler) CloseIssue(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, fmt.Sprintf("/issues/%s/%s/%d", owner, repo, index), http.StatusSeeOther)
 }
 
+// SetIssueState handles POST /issues/{owner}/{repo}/{index}/state.
+func (h *Handler) SetIssueState(w http.ResponseWriter, r *http.Request) {
+	token := getToken(r)
+	owner := r.PathValue("owner")
+	repo := r.PathValue("repo")
+	indexStr := r.PathValue("index")
+
+	index, err := strconv.ParseInt(indexStr, 10, 64)
+	if err != nil {
+		http.Error(w, "invalid issue index", http.StatusBadRequest)
+		return
+	}
+
+	if err := r.ParseForm(); err != nil {
+		http.Error(w, "bad request", http.StatusBadRequest)
+		return
+	}
+
+	state := r.FormValue("state")
+	if state != "open" && state != "closed" {
+		http.Error(w, "state must be 'open' or 'closed'", http.StatusBadRequest)
+		return
+	}
+
+	if err := h.Client.SetIssueState(r.Context(), token, owner, repo, index, state); err != nil {
+		slog.Error("failed to set issue state", "error", err, "owner", owner, "repo", repo, "index", index, "state", state)
+		http.Error(w, "failed to update issue state", http.StatusInternalServerError)
+		return
+	}
+
+	if isHTMX(r) {
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		if state == "closed" {
+			fmt.Fprintf(w, `<span class="state-closed" id="issue-state">closed</span>
+<button class="btn btn-secondary" hx-post="/issues/%s/%s/%d/state" hx-vals='{"state":"open"}' hx-target="#state-section" hx-swap="innerHTML">Reopen Issue</button>`,
+				template.HTMLEscapeString(owner), template.HTMLEscapeString(repo), index)
+		} else {
+			fmt.Fprintf(w, `<span class="state-open" id="issue-state">open</span>
+<button class="btn btn-danger" hx-post="/issues/%s/%s/%d/state" hx-vals='{"state":"closed"}' hx-target="#state-section" hx-swap="innerHTML">Close Issue</button>`,
+				template.HTMLEscapeString(owner), template.HTMLEscapeString(repo), index)
+		}
+		return
+	}
+
+	http.Redirect(w, r, fmt.Sprintf("/issues/%s/%s/%d", owner, repo, index), http.StatusSeeOther)
+}
+
 // AddComment handles POST /issues/{owner}/{repo}/{index}/comment.
 func (h *Handler) AddComment(w http.ResponseWriter, r *http.Request) {
 	token := getToken(r)
diff --git a/internal/handlers/handlers_test.go b/internal/handlers/handlers_test.go
index af96f5a..659549c 100644
--- a/internal/handlers/handlers_test.go
+++ b/internal/handlers/handlers_test.go
@@ -135,6 +135,54 @@ func TestSubmitReview_MissingEventType(t *testing.T) {
 	}
 }
 
+func TestSetIssueState_InvalidState(t *testing.T) {
+	h := newTestHandler()
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/state", h.SetIssueState)
+
+	req := httptest.NewRequest(http.MethodPost, "/issues/org/repo/1/state", nil)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusBadRequest)
+	}
+}
+
+func TestSetIssueState_InvalidIndex(t *testing.T) {
+	h := newTestHandler()
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/state", h.SetIssueState)
+
+	req := httptest.NewRequest(http.MethodPost, "/issues/org/repo/abc/state", nil)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusBadRequest)
+	}
+}
+
+func TestAddComment_EmptyBody(t *testing.T) {
+	h := newTestHandler()
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/comments", h.AddComment)
+
+	req := httptest.NewRequest(http.MethodPost, "/issues/org/repo/1/comments", nil)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusBadRequest)
+	}
+}
+
 func contains(s, substr string) bool {
 	return len(s) >= len(substr) && searchString(s, substr)
 }
diff --git a/internal/templates/issue_detail.html b/internal/templates/issue_detail.html
index 8ad3038..a997b1a 100644
--- a/internal/templates/issue_detail.html
+++ b/internal/templates/issue_detail.html
@@ -3,7 +3,15 @@
 
 <div class="card">
   <div class="card-meta">
-    <span class="state-open">{{.Issue.State}}</span>
+    <span id="state-section">
+      {{if eq .Issue.State "closed"}}
+      <span class="state-closed" id="issue-state">{{.Issue.State}}</span>
+      <button class="btn btn-secondary" hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/state" hx-vals='{"state":"open"}' hx-target="#state-section" hx-swap="innerHTML">Reopen Issue</button>
+      {{else}}
+      <span class="state-open" id="issue-state">{{.Issue.State}}</span>
+      <button class="btn btn-danger" hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/state" hx-vals='{"state":"closed"}' hx-target="#state-section" hx-swap="innerHTML">Close Issue</button>
+      {{end}}
+    </span>
     <span>{{.Issue.RepoOwner}}/{{.Issue.RepoName}} #{{.Issue.Number}}</span>
     {{range .Issue.Labels}}
     <span class="label" style="color:#{{.Color}};border:1px solid #{{.Color}}">{{.Name}}</span>
@@ -18,6 +26,7 @@
 
 {{if .Comments}}
 <h2>Comments</h2>
+<div id="comments-list">
 {{range .Comments}}
 <div class="comment">
   <div class="comment-header">
@@ -27,8 +36,19 @@
   <div class="comment-body">{{.Body}}</div>
 </div>
 {{end}}
+</div>
+{{else}}
+<div id="comments-list"></div>
 {{end}}
 
+<div class="card" style="margin-top:1rem;">
+  <h2>Add Comment</h2>
+  <form hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/comments" hx-target="#comments-list" hx-swap="beforeend" hx-on::after-request="if(event.detail.successful) this.reset()">
+    <textarea name="body" rows="4" placeholder="Write a comment..." required style="width:100%;margin-bottom:0.5rem;"></textarea>
+    <button type="submit" class="btn btn-primary" style="width:auto;padding:0.5rem 1rem;">Comment</button>
+  </form>
+</div>
+
 <div class="card" style="margin-top:1rem;">
   <h2>Actions</h2>
   <form hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/labels" hx-swap="outerHTML" style="margin-bottom:0.5rem;">