diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c9cf458..c2e185b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -4,6 +4,9 @@ on:
   push:
   workflow_dispatch:
 
+env:
+  FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
+
 jobs:
   unit-tests:
     name: Unit Tests
@@ -11,10 +14,10 @@ jobs:
 
     steps:
       - name: Check out repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v4.2.2
 
       - name: Set up Go
-        uses: actions/setup-go@v5
+        uses: actions/setup-go@v5.5.0
         with:
           go-version-file: go.mod
           cache: true
diff --git a/cmd/server/main.go b/cmd/server/main.go
index 71635ca..7282174 100644
--- a/cmd/server/main.go
+++ b/cmd/server/main.go
@@ -32,6 +32,7 @@ func main() {
 	defer service.Stop()
 
 	server := httpapi.NewServer(cfg, logger, dataStore)
+	server.SetTriggerer(service)
 
 	httpServer := &http.Server{
 		Addr:              cfg.ListenAddr,
diff --git a/internal/httpapi/dashboard.go b/internal/httpapi/dashboard.go
index ef87a79..6df6cd4 100644
--- a/internal/httpapi/dashboard.go
+++ b/internal/httpapi/dashboard.go
@@ -138,6 +138,25 @@ func (s *Server) handleDashboardCheckAction(w http.ResponseWriter, r *http.Reque
 
 	var paused bool
 	switch action {
+	case "trigger":
+		if s.triggerer == nil {
+			http.Error(w, "trigger not available", http.StatusNotImplemented)
+			return
+		}
+		if _, err := s.triggerer.RunNow(checkID); err != nil {
+			if errors.Is(err, store.ErrNotFound) {
+				http.NotFound(w, r)
+				return
+			}
+			http.Error(w, "failed to trigger check", http.StatusInternalServerError)
+			return
+		}
+		redirectTo := strings.TrimSpace(r.FormValue("redirect_to"))
+		if redirectTo == "" {
+			redirectTo = "/"
+		}
+		http.Redirect(w, r, redirectTo, http.StatusSeeOther)
+		return
 	case "pause":
 		paused = true
 	case "resume":
diff --git a/internal/httpapi/server.go b/internal/httpapi/server.go
index 7e1686c..7080125 100644
--- a/internal/httpapi/server.go
+++ b/internal/httpapi/server.go
@@ -9,14 +9,26 @@ import (
 	"strings"
 
 	"github.com/crleonard/pingtower/internal/config"
+	"github.com/crleonard/pingtower/internal/model"
 	"github.com/crleonard/pingtower/internal/store"
 )
 
+// Triggerer runs an on-demand check evaluation.
+type Triggerer interface {
+	RunNow(checkID string) (model.Result, error)
+}
+
 type Server struct {
-	cfg    config.Config
-	logger *log.Logger
-	store  store.Store
-	mux    *http.ServeMux
+	cfg       config.Config
+	logger    *log.Logger
+	store     store.Store
+	triggerer Triggerer
+	mux       *http.ServeMux
+}
+
+// SetTriggerer wires the monitor service so the trigger endpoint works.
+func (s *Server) SetTriggerer(t Triggerer) {
+	s.triggerer = t
 }
 
 type createCheckRequest struct {
@@ -48,6 +60,7 @@ func (s *Server) routes() {
 	s.mux.HandleFunc("POST /dashboard/checks", s.handleCreateCheckForm)
 	s.mux.HandleFunc("POST /dashboard/checks/", s.handleDashboardCheckAction)
 	s.mux.HandleFunc("GET /checks/", s.handleCheckSubresource)
+	s.mux.HandleFunc("POST /checks/", s.handleCheckPOSTSubresource)
 	s.mux.HandleFunc("GET /health", s.handleHealth)
 	s.mux.HandleFunc("GET /checks", s.handleListChecks)
 	s.mux.HandleFunc("POST /checks", s.handleCreateCheck)
@@ -187,6 +200,37 @@ func (s *Server) handleDeleteCheck(w http.ResponseWriter, _ *http.Request, check
 	w.WriteHeader(http.StatusNoContent)
 }
 
+func (s *Server) handleCheckPOSTSubresource(w http.ResponseWriter, r *http.Request) {
+	path := strings.TrimPrefix(r.URL.Path, "/checks/")
+	parts := strings.Split(strings.Trim(path, "/"), "/")
+	if len(parts) != 2 || parts[0] == "" {
+		http.NotFound(w, r)
+		return
+	}
+	if parts[1] == "trigger" {
+		s.handleTriggerCheck(w, r, parts[0])
+		return
+	}
+	http.NotFound(w, r)
+}
+
+func (s *Server) handleTriggerCheck(w http.ResponseWriter, _ *http.Request, checkID string) {
+	if s.triggerer == nil {
+		writeError(w, http.StatusNotImplemented, "trigger not available")
+		return
+	}
+	result, err := s.triggerer.RunNow(checkID)
+	if err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			writeError(w, http.StatusNotFound, "check not found")
+			return
+		}
+		writeError(w, http.StatusInternalServerError, "failed to trigger check")
+		return
+	}
+	writeJSON(w, http.StatusOK, result)
+}
+
 func (s *Server) loggingMiddleware(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		rec := &statusRecorder{ResponseWriter: w, statusCode: http.StatusOK}
diff --git a/internal/httpapi/server_test.go b/internal/httpapi/server_test.go
index f32c5a9..2f99c98 100644
--- a/internal/httpapi/server_test.go
+++ b/internal/httpapi/server_test.go
@@ -201,3 +201,137 @@ func TestDeleteCheckViaDashboard(t *testing.T) {
 		t.Fatalf("GetCheck() error = %v, want ErrNotFound", err)
 	}
 }
+
+func TestTriggerCheckAPI(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	dataStore, err := store.NewFileStore(filepath.Join(dir, "pingtower.json"))
+	if err != nil {
+		t.Fatalf("NewFileStore() error = %v", err)
+	}
+
+	created, err := dataStore.CreateCheck(model.Check{
+		Name:               "Trigger Test",
+		URL:                "https://example.com",
+		IntervalSeconds:    60,
+		TimeoutSeconds:     5,
+		ExpectedStatusCode: 200,
+	})
+	if err != nil {
+		t.Fatalf("CreateCheck() error = %v", err)
+	}
+
+	server := NewServer(config.Load(), log.New(io.Discard, "", 0), dataStore)
+	server.SetTriggerer(&stubTriggerer{result: model.Result{
+		CheckID: created.ID,
+		Status:  "healthy",
+	}})
+
+	req := httptest.NewRequest(http.MethodPost, "/checks/"+created.ID+"/trigger", nil)
+	res := httptest.NewRecorder()
+	server.Handler().ServeHTTP(res, req)
+
+	if res.Code != http.StatusOK {
+		t.Fatalf("POST /checks/{id}/trigger status = %d, want %d", res.Code, http.StatusOK)
+	}
+
+	var result model.Result
+	if err := json.NewDecoder(res.Body).Decode(&result); err != nil {
+		t.Fatalf("decode result: %v", err)
+	}
+	if result.Status != "healthy" {
+		t.Fatalf("result.Status = %q, want %q", result.Status, "healthy")
+	}
+}
+
+func TestTriggerCheckAPI_NotFound(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	dataStore, err := store.NewFileStore(filepath.Join(dir, "pingtower.json"))
+	if err != nil {
+		t.Fatalf("NewFileStore() error = %v", err)
+	}
+
+	server := NewServer(config.Load(), log.New(io.Discard, "", 0), dataStore)
+	server.SetTriggerer(&stubTriggerer{err: store.ErrNotFound})
+
+	req := httptest.NewRequest(http.MethodPost, "/checks/nonexistent/trigger", nil)
+	res := httptest.NewRecorder()
+	server.Handler().ServeHTTP(res, req)
+
+	if res.Code != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d", res.Code, http.StatusNotFound)
+	}
+}
+
+func TestTriggerCheckAPI_NoTriggerer(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	dataStore, err := store.NewFileStore(filepath.Join(dir, "pingtower.json"))
+	if err != nil {
+		t.Fatalf("NewFileStore() error = %v", err)
+	}
+
+	server := NewServer(config.Load(), log.New(io.Discard, "", 0), dataStore)
+
+	req := httptest.NewRequest(http.MethodPost, "/checks/anything/trigger", nil)
+	res := httptest.NewRecorder()
+	server.Handler().ServeHTTP(res, req)
+
+	if res.Code != http.StatusNotImplemented {
+		t.Fatalf("status = %d, want %d", res.Code, http.StatusNotImplemented)
+	}
+}
+
+func TestTriggerCheckDashboard(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	dataStore, err := store.NewFileStore(filepath.Join(dir, "pingtower.json"))
+	if err != nil {
+		t.Fatalf("NewFileStore() error = %v", err)
+	}
+
+	created, err := dataStore.CreateCheck(model.Check{
+		Name:               "Dashboard Trigger Test",
+		URL:                "https://example.com",
+		IntervalSeconds:    60,
+		TimeoutSeconds:     5,
+		ExpectedStatusCode: 200,
+	})
+	if err != nil {
+		t.Fatalf("CreateCheck() error = %v", err)
+	}
+
+	server := NewServer(config.Load(), log.New(io.Discard, "", 0), dataStore)
+	server.SetTriggerer(&stubTriggerer{result: model.Result{
+		CheckID: created.ID,
+		Status:  "healthy",
+	}})
+
+	form := url.Values{"redirect_to": []string{"/checks/" + created.ID + "/view"}}
+	req := httptest.NewRequest(http.MethodPost, "/dashboard/checks/"+created.ID+"/trigger", bytes.NewBufferString(form.Encode()))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	res := httptest.NewRecorder()
+	server.Handler().ServeHTTP(res, req)
+
+	if res.Code != http.StatusSeeOther {
+		t.Fatalf("dashboard trigger status = %d, want %d", res.Code, http.StatusSeeOther)
+	}
+	if loc := res.Header().Get("Location"); loc != "/checks/"+created.ID+"/view" {
+		t.Fatalf("Location = %q, want detail page", loc)
+	}
+}
+
+// stubTriggerer is a test double for the Triggerer interface.
+type stubTriggerer struct {
+	result model.Result
+	err    error
+}
+
+func (s *stubTriggerer) RunNow(_ string) (model.Result, error) {
+	return s.result, s.err
+}
diff --git a/internal/httpapi/templates/detail.html b/internal/httpapi/templates/detail.html
index eeee88d..36b3212 100644
--- a/internal/httpapi/templates/detail.html
+++ b/internal/httpapi/templates/detail.html
@@ -224,6 +224,10 @@ <h2>Recent history</h2>
           <div class="row-meta">Server time: {{.CurrentTime}} • Refreshes every 10 seconds</div>
         </div>
         <div class="actions">
+          <form method="post" action="/dashboard/checks/{{.Check.ID}}/trigger">
+            <input type="hidden" name="redirect_to" value="/checks/{{.Check.ID}}/view">
+            <button type="submit">Check now</button>
+          </form>
           {{if .Check.Paused}}
           <form method="post" action="/dashboard/checks/{{.Check.ID}}/resume">
             <input type="hidden" name="redirect_to" value="/checks/{{.Check.ID}}/view">
diff --git a/internal/monitor/service.go b/internal/monitor/service.go
index 5532dae..6ea3c06 100644
--- a/internal/monitor/service.go
+++ b/internal/monitor/service.go
@@ -78,7 +78,18 @@ func (s *Service) tick() {
 	}
 }
 
-func (s *Service) evaluate(check model.Check) {
+// RunNow immediately evaluates a check by ID and returns the result.
+// Returns an error only for store failures (e.g. store.ErrNotFound); a
+// network failure to the monitored URL is captured as a "down" Result.
+func (s *Service) RunNow(checkID string) (model.Result, error) {
+	check, err := s.store.GetCheck(checkID)
+	if err != nil {
+		return model.Result{}, err
+	}
+	return s.evaluate(check), nil
+}
+
+func (s *Service) evaluate(check model.Check) model.Result {
 	timeout := time.Duration(check.TimeoutSeconds) * time.Second
 	ctx, cancel := context.WithTimeout(context.Background(), timeout)
 	defer cancel()
@@ -86,27 +97,29 @@ func (s *Service) evaluate(check model.Check) {
 	start := time.Now()
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, check.URL, nil)
 	if err != nil {
-		s.persistResult(check, model.Result{
+		result := model.Result{
 			CheckID:      check.ID,
 			CheckedAt:    time.Now().UTC(),
 			Status:       "down",
 			ResponseMS:   time.Since(start).Milliseconds(),
 			ErrorMessage: err.Error(),
-		})
-		return
+		}
+		s.persistResult(check, result)
+		return result
 	}
 	req.Header.Set("User-Agent", s.userAgent)
 
 	resp, err := s.httpClient.Do(req)
 	if err != nil {
-		s.persistResult(check, model.Result{
+		result := model.Result{
 			CheckID:      check.ID,
 			CheckedAt:    time.Now().UTC(),
 			Status:       "down",
 			ResponseMS:   time.Since(start).Milliseconds(),
 			ErrorMessage: err.Error(),
-		})
-		return
+		}
+		s.persistResult(check, result)
+		return result
 	}
 	defer resp.Body.Close()
 
@@ -116,14 +129,16 @@ func (s *Service) evaluate(check model.Check) {
 		status = "down"
 	}
 
-	s.persistResult(check, model.Result{
+	result := model.Result{
 		CheckID:        check.ID,
 		CheckedAt:      time.Now().UTC(),
 		Status:         status,
 		StatusCode:     resp.StatusCode,
 		ResponseMS:     time.Since(start).Milliseconds(),
 		ResponseSample: strings.TrimSpace(string(body)),
-	})
+	}
+	s.persistResult(check, result)
+	return result
 }
 
 func (s *Service) persistResult(check model.Check, result model.Result) {
diff --git a/internal/monitor/service_test.go b/internal/monitor/service_test.go
new file mode 100644
index 0000000..d40825c
--- /dev/null
+++ b/internal/monitor/service_test.go
@@ -0,0 +1,105 @@
+package monitor
+
+import (
+	"io"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"path/filepath"
+	"testing"
+
+	"github.com/crleonard/pingtower/internal/model"
+	"github.com/crleonard/pingtower/internal/store"
+)
+
+func newTestService(t *testing.T) (*Service, store.Store) {
+	t.Helper()
+	dataStore, err := store.NewFileStore(filepath.Join(t.TempDir(), "pingtower.json"))
+	if err != nil {
+		t.Fatalf("NewFileStore() error = %v", err)
+	}
+	return NewService(dataStore, log.New(io.Discard, "", 0), "pingtower-test", 10), dataStore
+}
+
+func TestRunNow_Healthy(t *testing.T) {
+	t.Parallel()
+
+	target := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer target.Close()
+
+	svc, dataStore := newTestService(t)
+
+	check, err := dataStore.CreateCheck(model.Check{
+		Name:               "RunNow healthy",
+		URL:                target.URL,
+		IntervalSeconds:    60,
+		TimeoutSeconds:     5,
+		ExpectedStatusCode: http.StatusOK,
+	})
+	if err != nil {
+		t.Fatalf("CreateCheck() error = %v", err)
+	}
+
+	result, err := svc.RunNow(check.ID)
+	if err != nil {
+		t.Fatalf("RunNow() error = %v", err)
+	}
+	if result.Status != "healthy" {
+		t.Fatalf("Status = %q, want %q", result.Status, "healthy")
+	}
+	if result.StatusCode != http.StatusOK {
+		t.Fatalf("StatusCode = %d, want %d", result.StatusCode, http.StatusOK)
+	}
+
+	// result should also be persisted in the store
+	stored, err := dataStore.GetCheck(check.ID)
+	if err != nil {
+		t.Fatalf("GetCheck() error = %v", err)
+	}
+	if stored.LastStatus != "healthy" {
+		t.Fatalf("LastStatus = %q, want %q", stored.LastStatus, "healthy")
+	}
+}
+
+func TestRunNow_Down(t *testing.T) {
+	t.Parallel()
+
+	target := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusServiceUnavailable)
+	}))
+	defer target.Close()
+
+	svc, dataStore := newTestService(t)
+
+	check, err := dataStore.CreateCheck(model.Check{
+		Name:               "RunNow down",
+		URL:                target.URL,
+		IntervalSeconds:    60,
+		TimeoutSeconds:     5,
+		ExpectedStatusCode: http.StatusOK,
+	})
+	if err != nil {
+		t.Fatalf("CreateCheck() error = %v", err)
+	}
+
+	result, err := svc.RunNow(check.ID)
+	if err != nil {
+		t.Fatalf("RunNow() error = %v", err)
+	}
+	if result.Status != "down" {
+		t.Fatalf("Status = %q, want %q", result.Status, "down")
+	}
+}
+
+func TestRunNow_NotFound(t *testing.T) {
+	t.Parallel()
+
+	svc, _ := newTestService(t)
+
+	_, err := svc.RunNow("nonexistent-id")
+	if err == nil {
+		t.Fatal("RunNow() expected error for unknown ID, got nil")
+	}
+}