diff --git a/main.go b/main.go
index b5599b4..90d9f66 100644
--- a/main.go
+++ b/main.go
@@ -40,6 +40,9 @@ func parseConfig() (c config.Config) {
 	fs.StringVar(&c.StaticFiles, "static-files", "client", "Location of the static files to serve (index.html, etc.)")
 	fs.IntVar(&c.HistoryMaxRetention, "history-retention", 0, "Maximum number of calls to keep in the history per session (0 = no limit)")
 	fs.StringVar(&c.PersistenceDirectory, "persistence-directory", "", "If defined, the directory where the sessions will be synchronized")
+	fs.StringVar(&c.InitMocks, "init-mocks", "",
+		"If set, load mocks from a YAML file (POST /mocks format) into a session at startup; "+
+			"mutually exclusive with --persistence-directory")
 	fs.BoolVar(&c.TLSEnable, "tls-enable", false, "Enable TLS using the provided certificate")
 	fs.StringVar(&c.TLSCertFile, "tls-cert-file", "/etc/smocker/tls/certs/cert.pem", "Path to TLS certificate file ")
 	fs.StringVar(&c.TLSKeyFile, "tls-private-key-file", "/etc/smocker/tls/private/key.pem", "Path to TLS key file")
@@ -104,5 +107,15 @@ func setupLogger(logLevel string) {
 func main() {
 	c := parseConfig()
 	setupLogger(c.LogLevel)
+
+	// Loading mocks at startup and persisting sessions are opposite intents: a seed file is a
+	// fixed, read-only starting point, while persistence resumes (and rewrites) whatever state it
+	// last held. Both define the boot state, so allowing both would be ambiguous on restart.
+	if c.InitMocks != "" && c.PersistenceDirectory != "" {
+		slog.Error("--init-mocks and --persistence-directory are mutually exclusive: " +
+			"seed mocks from a file (ephemeral) or persist sessions to a directory, not both")
+		os.Exit(1)
+	}
+
 	server.Serve(c)
 }
diff --git a/server/config/config.go b/server/config/config.go
index b2212e7..68c11db 100644
--- a/server/config/config.go
+++ b/server/config/config.go
@@ -8,6 +8,7 @@ type Config struct {
 	StaticFiles          string
 	HistoryMaxRetention  int
 	PersistenceDirectory string
+	InitMocks            string
 	TLSEnable            bool
 	TLSCertFile          string
 	TLSKeyFile           string
diff --git a/server/mock_server.go b/server/mock_server.go
index ebc9c69..7248198 100644
--- a/server/mock_server.go
+++ b/server/mock_server.go
@@ -3,6 +3,7 @@ package server
 import (
 	"log/slog"
 	"net/http"
+	"os"
 	"strconv"
 
 	"github.com/labstack/echo/v4"
@@ -18,7 +19,11 @@ func NewMockServer(cfg config.Config) (*http.Server, services.Mocks) {
 	if err != nil {
 		slog.Error("Unable to load sessions", "error", err)
 	}
-	mockServices := services.NewMocks(sessions, cfg.HistoryMaxRetention, persistence)
+	mockServices, err := services.NewMocks(sessions, cfg.HistoryMaxRetention, persistence, cfg.InitMocks)
+	if err != nil {
+		slog.Error("Unable to load initial mocks", "error", err, "init-mocks", cfg.InitMocks)
+		os.Exit(1)
+	}
 
 	mockServerEngine.HideBanner = true
 	mockServerEngine.HidePort = true
diff --git a/server/services/mocks.go b/server/services/mocks.go
index c762cf5..57779cf 100644
--- a/server/services/mocks.go
+++ b/server/services/mocks.go
@@ -2,12 +2,15 @@ package services
 
 import (
 	"fmt"
+	"log/slog"
+	"os"
 	"regexp"
 	"strings"
 	"sync"
 	"time"
 
 	"github.com/smocker-dev/smocker/server/types"
+	"gopkg.in/yaml.v3"
 )
 
 var (
@@ -44,7 +47,7 @@ type mocks struct {
 	persistence      Persistence
 }
 
-func NewMocks(sessions types.Sessions, historyRetention int, persistence Persistence) Mocks {
+func NewMocks(sessions types.Sessions, historyRetention int, persistence Persistence, initMocksFile string) (Mocks, error) {
 	s := &mocks{
 		sessions:         types.Sessions{},
 		historyRetention: historyRetention,
@@ -53,7 +56,42 @@ func NewMocks(sessions types.Sessions, historyRetention int, persistence Persist
 	if sessions != nil {
 		s.sessions = sessions
 	}
-	return s
+	if initMocksFile != "" {
+		if err := s.seedFromFile(initMocksFile); err != nil {
+			return nil, err
+		}
+	}
+	return s, nil
+}
+
+// seedFromFile loads mocks from a YAML file (the POST /mocks format) into a fresh "init-mocks"
+// session. Backs the --init-mocks startup flag; the mocks are never written back.
+func (s *mocks) seedFromFile(path string) error {
+	file, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	var loaded types.Mocks
+	if err := yaml.NewDecoder(file).Decode(&loaded); err != nil {
+		return err
+	}
+	for _, mock := range loaded {
+		if err := mock.Validate(); err != nil {
+			return err
+		}
+	}
+
+	sessionID := s.NewSession("init-mocks").ID
+	for _, mock := range loaded {
+		if _, err := s.AddMock(sessionID, mock); err != nil {
+			return err
+		}
+	}
+
+	slog.Info("Loaded initial mocks", "count", len(loaded), "init-mocks", path)
+	return nil
 }
 
 func (s *mocks) AddMock(sessionID string, newMock *types.Mock) (*types.Mock, error) {
diff --git a/server/services/mocks_test.go b/server/services/mocks_test.go
index 55d4bd7..828373e 100644
--- a/server/services/mocks_test.go
+++ b/server/services/mocks_test.go
@@ -1,12 +1,23 @@
 package services
 
 import (
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/smocker-dev/smocker/server/types"
 	"gopkg.in/yaml.v3"
 )
 
+func newTestMocks(t *testing.T) Mocks {
+	t.Helper()
+	svc, err := NewMocks(nil, 0, NewPersistence(""), "")
+	if err != nil {
+		t.Fatalf("NewMocks: %v", err)
+	}
+	return svc
+}
+
 func mockFromYAML(t *testing.T, s string) *types.Mock {
 	t.Helper()
 	var m types.Mock
@@ -16,10 +27,69 @@ func mockFromYAML(t *testing.T, s string) *types.Mock {
 	return &m
 }
 
+// TestNewMocksInitFile covers the --init-mocks path: a YAML file of mocks (the POST /mocks format)
+// is loaded into a fresh "init-mocks" session when the service is constructed.
+func TestNewMocksInitFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "mocks.yml")
+	content := `
+- request:
+    method: GET
+    path: /hello
+  response:
+    status: 200
+    body: hi
+- request:
+    method: GET
+    path: /health
+  response:
+    status: 204
+`
+	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	svc, err := NewMocks(nil, 0, NewPersistence(""), path)
+	if err != nil {
+		t.Fatalf("NewMocks: %v", err)
+	}
+
+	session := svc.GetLastSession()
+	if session == nil {
+		t.Fatal("expected a seeded session")
+	}
+	if session.Name != "init-mocks" {
+		t.Fatalf("expected the seeded session to be named %q, got %q", "init-mocks", session.Name)
+	}
+	mocks, err := svc.GetMocks(session.ID)
+	if err != nil {
+		t.Fatalf("GetMocks: %v", err)
+	}
+	if len(mocks) != 2 {
+		t.Fatalf("expected 2 seeded mocks, got %d", len(mocks))
+	}
+}
+
+func TestNewMocksInitFileMissing(t *testing.T) {
+	if _, err := NewMocks(nil, 0, NewPersistence(""), filepath.Join(t.TempDir(), "nope.yml")); err == nil {
+		t.Fatal("expected an error for a missing file")
+	}
+}
+
+func TestNewMocksInitFileInvalid(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "mocks.yml")
+	// A mock with neither response, proxy, nor dynamic_response fails Validate().
+	if err := os.WriteFile(path, []byte("- request: {path: /a}\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := NewMocks(nil, 0, NewPersistence(""), path); err == nil {
+		t.Fatal("expected a validation error for an incomplete mock")
+	}
+}
+
 // TestUpdateAndDeleteMock covers the happy path for the edit/delete feature (issues #299/#266/#303)
 // while the session history is still empty.
 func TestUpdateAndDeleteMock(t *testing.T) {
-	svc := NewMocks(nil, 0, NewPersistence(""))
+	svc := newTestMocks(t)
 	session := svc.NewSession("edit")
 
 	added, err := svc.AddMock(
@@ -71,7 +141,7 @@ func TestUpdateAndDeleteMock(t *testing.T) {
 
 // TestDeleteSession covers removing a single session and the not-found path.
 func TestDeleteSession(t *testing.T) {
-	svc := NewMocks(nil, 0, NewPersistence(""))
+	svc := newTestMocks(t)
 	keep := svc.NewSession("keep")
 	drop := svc.NewSession("drop")
 
@@ -95,7 +165,7 @@ func TestDeleteSession(t *testing.T) {
 // TestEditForbiddenOnceCalled locks the maintainers' position: once the session has received calls,
 // mocks are append-only (history entries are tied to the mock that answered them).
 func TestEditForbiddenOnceCalled(t *testing.T) {
-	svc := NewMocks(nil, 0, NewPersistence(""))
+	svc := newTestMocks(t)
 	session := svc.NewSession("called")
 	added, err := svc.AddMock(
 		session.ID,