diff --git a/cmd/server/main.go b/cmd/server/main.go
index b9e99bd..e0d649b 100644
--- a/cmd/server/main.go
+++ b/cmd/server/main.go
@@ -46,12 +46,7 @@ func run(cfg config.Config, logger *slog.Logger) error {
 
 	errc := make(chan error, 1)
 	go func() {
-		logger.Info("listening",
-			"addr", cfg.HTTPAddr,
-			"public_url", cfg.PublicURL.String(),
-			"data_dir", cfg.DataDir,
-			"version", version,
-		)
+		logListening(logger, cfg)
 		errc <- srv.ListenAndServe()
 	}()
 
@@ -72,3 +67,14 @@ func run(cfg config.Config, logger *slog.Logger) error {
 	}
 	return nil
 }
+
+// logListening logs the startup line. Only the public URL's origin is logged
+// so no credential-bearing URL component can reach the log.
+func logListening(logger *slog.Logger, cfg config.Config) {
+	logger.Info("listening",
+		"addr", cfg.HTTPAddr,
+		"public_origin", cfg.PublicOrigin(),
+		"data_dir", cfg.DataDir,
+		"version", version,
+	)
+}
diff --git a/cmd/server/main_test.go b/cmd/server/main_test.go
new file mode 100644
index 0000000..02748e8
--- /dev/null
+++ b/cmd/server/main_test.go
@@ -0,0 +1,34 @@
+package main
+
+import (
+	"bytes"
+	"log/slog"
+	"net/url"
+	"strings"
+	"testing"
+
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/config"
+)
+
+func TestLogListeningOmitsURLCredentials(t *testing.T) {
+	t.Parallel()
+
+	// Load rejects such URLs; this proves the log stays safe even if one
+	// reached the Config some other way.
+	u, err := url.Parse("https://alice:hunter2@meals.example.com/app?token=t0ken")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf bytes.Buffer
+	logListening(slog.New(slog.NewJSONHandler(&buf, nil)), config.Config{HTTPAddr: ":8080", PublicURL: u})
+
+	out := buf.String()
+	for _, leak := range []string{"alice", "hunter2", "t0ken"} {
+		if strings.Contains(out, leak) {
+			t.Errorf("startup log leaks %q: %s", leak, out)
+		}
+	}
+	if !strings.Contains(out, `"public_origin":"https://meals.example.com"`) {
+		t.Errorf("startup log missing public origin: %s", out)
+	}
+}
diff --git a/internal/config/config.go b/internal/config/config.go
index dd45f72..1e84b99 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -8,17 +8,18 @@ import (
 	"net"
 	"net/url"
 	"os"
+	"strconv"
 	"strings"
 	"time"
 )
 
 // Environment variable names.
 const (
-	EnvHTTPAddr          = "MEALQUEST_HTTP_ADDR"
-	EnvPublicURL         = "MEALQUEST_PUBLIC_URL"
-	EnvDataDir           = "MEALQUEST_DATA_DIR"
-	EnvShutdownTimeout   = "MEALQUEST_SHUTDOWN_TIMEOUT"
-	EnvSessionSecretFile = "MEALQUEST_SESSION_SECRET_FILE"
+	EnvHTTPAddr        = "MEALQUEST_HTTP_ADDR"
+	EnvPublicURL       = "MEALQUEST_PUBLIC_URL"
+	EnvDataDir         = "MEALQUEST_DATA_DIR"
+	EnvShutdownTimeout = "MEALQUEST_SHUTDOWN_TIMEOUT"
+	EnvSecretKeyFile   = "MEALQUEST_SECRET_KEY_FILE"
 )
 
 // Config is the validated service configuration.
@@ -27,7 +28,13 @@ type Config struct {
 	PublicURL       *url.URL
 	DataDir         string
 	ShutdownTimeout time.Duration
-	SessionSecret   Secret
+	SecretKey       Secret
+}
+
+// PublicOrigin returns the scheme and host of PublicURL, the only parts of it
+// that are safe to log.
+func (c Config) PublicOrigin() string {
+	return c.PublicURL.Scheme + "://" + c.PublicURL.Host
 }
 
 // Load reads and validates configuration from the process environment.
@@ -43,7 +50,7 @@ func load(lookup func(string) (string, bool)) (Config, error) {
 		PublicURL:       r.httpURL(EnvPublicURL),
 		DataDir:         r.dir(EnvDataDir),
 		ShutdownTimeout: r.duration(EnvShutdownTimeout),
-		SessionSecret:   r.secretFile(EnvSessionSecretFile),
+		SecretKey:       r.secretFile(EnvSecretKeyFile),
 	}
 	if len(r.problems) > 0 {
 		return Config{}, &Error{Problems: r.problems}
@@ -112,10 +119,15 @@ func (r *reader) listenAddr(name string) string {
 	if !ok {
 		return ""
 	}
-	if _, _, err := net.SplitHostPort(v); err != nil {
+	_, port, err := net.SplitHostPort(v)
+	if err != nil {
 		r.fail(name, "invalid listen address %q (want host:port or :port)", v)
 		return ""
 	}
+	if _, err := strconv.ParseUint(port, 10, 16); err != nil {
+		r.fail(name, "invalid port %q in listen address (want 0-65535)", port)
+		return ""
+	}
 	return v
 }
 
@@ -124,9 +136,14 @@ func (r *reader) httpURL(name string) *url.URL {
 	if !ok {
 		return nil
 	}
+	// The value is never echoed: it may carry credentials.
 	u, err := url.Parse(v)
 	if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
-		r.fail(name, "invalid URL %q (want absolute http:// or https:// URL)", v)
+		r.fail(name, "invalid URL (want absolute http:// or https:// URL)")
+		return nil
+	}
+	if u.User != nil {
+		r.fail(name, "URL must not contain user credentials")
 		return nil
 	}
 	return u
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index b617872..ebaafa2 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -3,6 +3,7 @@ package config
 import (
 	"errors"
 	"fmt"
+	"net/url"
 	"os"
 	"path/filepath"
 	"slices"
@@ -15,7 +16,7 @@ func TestLoad(t *testing.T) {
 	t.Parallel()
 
 	dir := t.TempDir()
-	secretPath := filepath.Join(dir, "session_secret")
+	secretPath := filepath.Join(dir, "secret_key")
 	if err := os.WriteFile(secretPath, []byte("s3cret-value\n"), 0o600); err != nil {
 		t.Fatal(err)
 	}
@@ -27,11 +28,11 @@ func TestLoad(t *testing.T) {
 
 	valid := func() map[string]string {
 		return map[string]string{
-			EnvHTTPAddr:          ":8080",
-			EnvPublicURL:         "https://meals.example.com",
-			EnvDataDir:           dir,
-			EnvShutdownTimeout:   "15s",
-			EnvSessionSecretFile: secretPath,
+			EnvHTTPAddr:        ":8080",
+			EnvPublicURL:       "https://meals.example.com",
+			EnvDataDir:         dir,
+			EnvShutdownTimeout: "15s",
+			EnvSecretKeyFile:   secretPath,
 		}
 	}
 	with := func(changes map[string]string, unset ...string) map[string]string {
@@ -68,7 +69,7 @@ func TestLoad(t *testing.T) {
 			name: "all missing are collected",
 			env:  map[string]string{},
 			badVars: []string{
-				EnvHTTPAddr, EnvPublicURL, EnvDataDir, EnvShutdownTimeout, EnvSessionSecretFile,
+				EnvHTTPAddr, EnvPublicURL, EnvDataDir, EnvShutdownTimeout, EnvSecretKeyFile,
 			},
 		},
 		{
@@ -86,6 +87,21 @@ func TestLoad(t *testing.T) {
 			env:     with(map[string]string{EnvHTTPAddr: "8080"}),
 			badVars: []string{EnvHTTPAddr},
 		},
+		{
+			name:    "non-numeric port",
+			env:     with(map[string]string{EnvHTTPAddr: ":notaport"}),
+			badVars: []string{EnvHTTPAddr},
+		},
+		{
+			name:    "empty port",
+			env:     with(map[string]string{EnvHTTPAddr: "127.0.0.1:"}),
+			badVars: []string{EnvHTTPAddr},
+		},
+		{
+			name:    "port out of range",
+			env:     with(map[string]string{EnvHTTPAddr: ":65536"}),
+			badVars: []string{EnvHTTPAddr},
+		},
 		{
 			name:    "relative public URL",
 			env:     with(map[string]string{EnvPublicURL: "meals.example.com"}),
@@ -98,31 +114,31 @@ func TestLoad(t *testing.T) {
 		},
 		{
 			name:    "unreadable secret file",
-			env:     with(map[string]string{EnvSessionSecretFile: unreadablePath}),
-			badVars: []string{EnvSessionSecretFile},
+			env:     with(map[string]string{EnvSecretKeyFile: unreadablePath}),
+			badVars: []string{EnvSecretKeyFile},
 		},
 		{
 			name:    "secret file path is a directory",
-			env:     with(map[string]string{EnvSessionSecretFile: dir}),
-			badVars: []string{EnvSessionSecretFile},
+			env:     with(map[string]string{EnvSecretKeyFile: dir}),
+			badVars: []string{EnvSecretKeyFile},
 		},
 		{
 			name:    "empty secret file",
-			env:     with(map[string]string{EnvSessionSecretFile: emptyPath}),
-			badVars: []string{EnvSessionSecretFile},
+			env:     with(map[string]string{EnvSecretKeyFile: emptyPath}),
+			badVars: []string{EnvSecretKeyFile},
 		},
 		{
 			name:    "inline secret rejected",
-			env:     with(map[string]string{"MEALQUEST_SESSION_SECRET": "inline"}),
-			badVars: []string{"MEALQUEST_SESSION_SECRET"},
+			env:     with(map[string]string{"MEALQUEST_SECRET_KEY": "inline"}),
+			badVars: []string{"MEALQUEST_SECRET_KEY"},
 		},
 		{
 			name: "several invalid values are all named",
 			env: with(map[string]string{
-				EnvShutdownTimeout:   "soon",
-				EnvSessionSecretFile: unreadablePath,
+				EnvShutdownTimeout: "soon",
+				EnvSecretKeyFile:   unreadablePath,
 			}, EnvPublicURL),
-			badVars: []string{EnvPublicURL, EnvShutdownTimeout, EnvSessionSecretFile},
+			badVars: []string{EnvPublicURL, EnvShutdownTimeout, EnvSecretKeyFile},
 		},
 	}
 
@@ -169,16 +185,16 @@ func TestLoadValues(t *testing.T) {
 	t.Parallel()
 
 	dir := t.TempDir()
-	secretPath := filepath.Join(dir, "session_secret")
+	secretPath := filepath.Join(dir, "secret_key")
 	if err := os.WriteFile(secretPath, []byte("s3cret-value\r\n"), 0o600); err != nil {
 		t.Fatal(err)
 	}
 	env := map[string]string{
-		EnvHTTPAddr:          "127.0.0.1:9000",
-		EnvPublicURL:         "http://localhost:9000",
-		EnvDataDir:           dir,
-		EnvShutdownTimeout:   "1m30s",
-		EnvSessionSecretFile: secretPath,
+		EnvHTTPAddr:        "127.0.0.1:9000",
+		EnvPublicURL:       "http://localhost:9000",
+		EnvDataDir:         dir,
+		EnvShutdownTimeout: "1m30s",
+		EnvSecretKeyFile:   secretPath,
 	}
 	cfg, err := load(func(k string) (string, bool) { v, ok := env[k]; return v, ok })
 	if err != nil {
@@ -197,8 +213,8 @@ func TestLoadValues(t *testing.T) {
 	if cfg.ShutdownTimeout != 90*time.Second {
 		t.Errorf("ShutdownTimeout = %v, want 1m30s", cfg.ShutdownTimeout)
 	}
-	if cfg.SessionSecret.Reveal() != "s3cret-value" {
-		t.Errorf("SessionSecret.Reveal() = %q, want trailing newline trimmed", cfg.SessionSecret.Reveal())
+	if cfg.SecretKey.Reveal() != "s3cret-value" {
+		t.Errorf("SecretKey.Reveal() = %q, want trailing newline trimmed", cfg.SecretKey.Reveal())
 	}
 }
 
@@ -207,7 +223,7 @@ func TestSecretRedacted(t *testing.T) {
 
 	s := Secret{value: "s3cret-value"}
 	for _, format := range []string{"%v", "%s", "%+v", "%#v"} {
-		cfg := Config{SessionSecret: s}
+		cfg := Config{SecretKey: s}
 		for _, out := range []string{fmt.Sprintf(format, s), fmt.Sprintf(format, cfg)} {
 			if strings.Contains(out, "s3cret-value") {
 				t.Errorf("format %s leaked secret: %s", format, out)
@@ -215,3 +231,36 @@ func TestSecretRedacted(t *testing.T) {
 		}
 	}
 }
+
+func TestPublicURLWithCredentialsRejected(t *testing.T) {
+	t.Parallel()
+
+	for _, raw := range []string{
+		"https://alice:hunter2@example.com",
+		"https://alice@example.com",
+		"https://alice:hunter2@[bad",
+	} {
+		env := map[string]string{EnvPublicURL: raw}
+		_, err := load(func(k string) (string, bool) { v, ok := env[k]; return v, ok })
+
+		var cerr *Error
+		if !errors.As(err, &cerr) || !slices.ContainsFunc(cerr.Problems, func(p Problem) bool { return p.Var == EnvPublicURL }) {
+			t.Errorf("load(%q) error = %v, want problem for %s", raw, err, EnvPublicURL)
+		}
+		if err != nil && (strings.Contains(err.Error(), "hunter2") || strings.Contains(err.Error(), "alice")) {
+			t.Errorf("load(%q) error leaks credentials: %v", raw, err)
+		}
+	}
+}
+
+func TestPublicOrigin(t *testing.T) {
+	t.Parallel()
+
+	u, err := url.Parse("https://alice:hunter2@meals.example.com:8443/app?token=x#frag")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := (Config{PublicURL: u}).PublicOrigin(), "https://meals.example.com:8443"; got != want {
+		t.Errorf("PublicOrigin() = %q, want %q", got, want)
+	}
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index fa4f203..597e456 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -14,9 +14,37 @@ import (
 func NewRouter(logger *slog.Logger, version string) http.Handler {
 	r := chi.NewRouter()
 	r.Get("/health", health(logger, version))
+	r.MethodNotAllowed(methodNotAllowed(logger))
 	return r
 }
 
+type errorBody struct {
+	Error apiError `json:"error"`
+}
+
+type apiError struct {
+	Code      string `json:"code"`
+	Message   string `json:"message"`
+	Retryable bool   `json:"retryable"`
+}
+
+func methodNotAllowed(logger *slog.Logger) http.HandlerFunc {
+	body, err := json.Marshal(errorBody{Error: apiError{
+		Code:    "method_not_allowed",
+		Message: "method not allowed",
+	}})
+	if err != nil {
+		panic(err) // fixed string and bool fields cannot fail to marshal
+	}
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusMethodNotAllowed)
+		if _, err := w.Write(body); err != nil {
+			logger.WarnContext(r.Context(), "write method not allowed response", "error", err)
+		}
+	}
+}
+
 type healthResponse struct {
 	Status  string `json:"status"`
 	Version string `json:"version"`
diff --git a/internal/server/server_test.go b/internal/server/server_test.go
index 0e7e9f9..b79856e 100644
--- a/internal/server/server_test.go
+++ b/internal/server/server_test.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"io"
 	"log/slog"
+	"maps"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -48,4 +49,21 @@ func TestHealthRejectsOtherMethods(t *testing.T) {
 	if rec.Code != http.StatusMethodNotAllowed {
 		t.Errorf("status = %d, want 405", rec.Code)
 	}
+	if ct := rec.Header().Get("Content-Type"); ct != "application/json" {
+		t.Errorf("Content-Type = %q, want application/json", ct)
+	}
+	var got struct {
+		Error map[string]any `json:"error"`
+	}
+	if err := json.NewDecoder(rec.Body).Decode(&got); err != nil {
+		t.Fatal(err)
+	}
+	want := map[string]any{
+		"code":      "method_not_allowed",
+		"message":   "method not allowed",
+		"retryable": false,
+	}
+	if !maps.Equal(got.Error, want) {
+		t.Errorf("error body = %v, want %v", got.Error, want)
+	}
 }