diff --git a/internal/logger/context.go b/internal/logger/context.go
index a50bf2a1a..292981645 100644
--- a/internal/logger/context.go
+++ b/internal/logger/context.go
@@ -14,7 +14,7 @@ type key string
 
 var cidKey key = "cid.srsx.ossrs.org"
 
-// generateContextID generates a random context id in string.
+// GenerateContextID generates a random context id in string.
 func GenerateContextID() string {
 	randomBytes := make([]byte, 32)
 	_, _ = rand.Read(randomBytes)
@@ -26,11 +26,11 @@ func GenerateContextID() string {
 
 // WithContext creates a new context with cid, which will be used for log.
 func WithContext(ctx context.Context) context.Context {
-	return WithContextID(ctx, GenerateContextID())
+	return withContextID(ctx, GenerateContextID())
 }
 
-// WithContextID creates a new context with cid, which will be used for log.
-func WithContextID(ctx context.Context, cid string) context.Context {
+// withContextID creates a new context with cid, which will be used for log.
+func withContextID(ctx context.Context, cid string) context.Context {
 	return context.WithValue(ctx, cidKey, cid)
 }
 
diff --git a/internal/logger/context_test.go b/internal/logger/context_test.go
new file mode 100644
index 000000000..2adda9538
--- /dev/null
+++ b/internal/logger/context_test.go
@@ -0,0 +1,82 @@
+// Copyright (c) 2026 Winlin
+//
+// SPDX-License-Identifier: MIT
+package logger
+
+import (
+	"context"
+	"encoding/hex"
+	"testing"
+)
+
+func TestGenerateContextID_LengthAndHex(t *testing.T) {
+	cid := GenerateContextID()
+	if len(cid) != 7 {
+		t.Fatalf("len(cid) = %d, want 7", len(cid))
+	}
+	if _, err := hex.DecodeString(cid + "0"); err != nil {
+		t.Fatalf("cid %q is not hex: %v", cid, err)
+	}
+}
+
+func TestGenerateContextID_Unique(t *testing.T) {
+	seen := make(map[string]struct{}, 1000)
+	for i := range 1000 {
+		cid := GenerateContextID()
+		if _, dup := seen[cid]; dup {
+			t.Fatalf("duplicate cid %q at iteration %d", cid, i)
+		}
+		seen[cid] = struct{}{}
+	}
+}
+
+func TestWithContext_AttachesCID(t *testing.T) {
+	ctx := WithContext(context.Background())
+	cid := ContextID(ctx)
+	if len(cid) != 7 {
+		t.Fatalf("ContextID length = %d, want 7", len(cid))
+	}
+}
+
+func TestWithContext_IndependentCIDs(t *testing.T) {
+	c1 := WithContext(context.Background())
+	c2 := WithContext(context.Background())
+	if ContextID(c1) == ContextID(c2) {
+		t.Fatalf("expected distinct cids, got %q twice", ContextID(c1))
+	}
+}
+
+func TestContextID_Missing(t *testing.T) {
+	if got := ContextID(context.Background()); got != "" {
+		t.Fatalf("ContextID on empty ctx = %q, want \"\"", got)
+	}
+}
+
+func TestContextID_WrongTypeReturnsEmpty(t *testing.T) {
+	ctx := context.WithValue(context.Background(), cidKey, 42)
+	if got := ContextID(ctx); got != "" {
+		t.Fatalf("ContextID with int value = %q, want \"\"", got)
+	}
+}
+
+func TestWithContextID_RoundTrip(t *testing.T) {
+	ctx := withContextID(context.Background(), "abcdef1")
+	if got := ContextID(ctx); got != "abcdef1" {
+		t.Fatalf("ContextID = %q, want %q", got, "abcdef1")
+	}
+}
+
+func TestWithContextID_Overwrite(t *testing.T) {
+	ctx := withContextID(context.Background(), "first00")
+	ctx = withContextID(ctx, "second1")
+	if got := ContextID(ctx); got != "second1" {
+		t.Fatalf("ContextID after overwrite = %q, want %q", got, "second1")
+	}
+}
+
+func TestCIDKey_NotCollidingWithPlainString(t *testing.T) {
+	ctx := context.WithValue(context.Background(), string(cidKey), "plain")
+	if got := ContextID(ctx); got != "" {
+		t.Fatalf("ContextID leaked through string key = %q, want \"\"", got)
+	}
+}
diff --git a/internal/logger/log.go b/internal/logger/log.go
index 9653c0846..f710653e5 100644
--- a/internal/logger/log.go
+++ b/internal/logger/log.go
@@ -5,8 +5,9 @@ package logger
 
 import (
 	"context"
-	"io/ioutil"
-	stdLog "log"
+	"fmt"
+	"io"
+	"log/slog"
 	"os"
 )
 
@@ -15,8 +16,8 @@ type logger interface {
 }
 
 type loggerPlus struct {
-	logger *stdLog.Logger
-	level  string
+	logger *slog.Logger
+	level  slog.Level
 }
 
 func newLoggerPlus(opts ...func(*loggerPlus)) *loggerPlus {
@@ -27,61 +28,95 @@ func newLoggerPlus(opts ...func(*loggerPlus)) *loggerPlus {
 	return v
 }
 
-func (v *loggerPlus) Printf(ctx context.Context, f string, a ...interface{}) {
-	format, args := f, a
+func (v *loggerPlus) Printf(ctx context.Context, f string, a ...any) {
+	attrs := []slog.Attr{slog.Int("pid", os.Getpid())}
 	if cid := ContextID(ctx); cid != "" {
-		format, args = "[%v][%v][%v] "+format, append([]interface{}{v.level, os.Getpid(), cid}, a...)
+		attrs = append(attrs, slog.String("cid", cid))
 	}
-
-	v.logger.Printf(format, args...)
+	v.logger.LogAttrs(ctx, v.level, fmt.Sprintf(f, a...), attrs...)
 }
 
 var verboseLogger logger
 
-func Vf(ctx context.Context, format string, a ...interface{}) {
+func Vf(ctx context.Context, format string, a ...any) {
 	verboseLogger.Printf(ctx, format, a...)
 }
 
 var debugLogger logger
 
-func Df(ctx context.Context, format string, a ...interface{}) {
+func Df(ctx context.Context, format string, a ...any) {
 	debugLogger.Printf(ctx, format, a...)
 }
 
 var warnLogger logger
 
-func Wf(ctx context.Context, format string, a ...interface{}) {
+func Wf(ctx context.Context, format string, a ...any) {
 	warnLogger.Printf(ctx, format, a...)
 }
 
 var errorLogger logger
 
-func Ef(ctx context.Context, format string, a ...interface{}) {
+func Ef(ctx context.Context, format string, a ...any) {
 	errorLogger.Printf(ctx, format, a...)
 }
 
 const (
-	logVerboseLabel = "verb"
-	logDebugLabel   = "debug"
-	logWarnLabel    = "warn"
-	logErrorLabel   = "error"
+	levelVerb  slog.Level = slog.LevelDebug - 4
+	levelDebug slog.Level = slog.LevelDebug
+	levelWarn  slog.Level = slog.LevelWarn
+	levelError slog.Level = slog.LevelError
 )
 
+// newJSONLogger builds a slog.Logger that writes JSON records to w, renders the
+// time in UTC, and maps our custom levels to short lowercase labels.
+func newJSONLogger(w io.Writer) *slog.Logger {
+	h := slog.NewJSONHandler(w, &slog.HandlerOptions{
+		Level: levelVerb,
+		ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
+			if len(groups) != 0 {
+				return a
+			}
+			switch a.Key {
+			case slog.TimeKey:
+				return slog.Time(slog.TimeKey, a.Value.Time().UTC())
+			case slog.LevelKey:
+				return slog.String(slog.LevelKey, levelLabel(a.Value.Any().(slog.Level)))
+			}
+			return a
+		},
+	})
+	return slog.New(h)
+}
+
+func levelLabel(l slog.Level) string {
+	switch l {
+	case levelVerb:
+		return "verb"
+	case levelDebug:
+		return "debug"
+	case levelWarn:
+		return "warn"
+	case levelError:
+		return "error"
+	}
+	return l.String()
+}
+
 func init() {
-	verboseLogger = newLoggerPlus(func(logger *loggerPlus) {
-		logger.logger = stdLog.New(ioutil.Discard, "", stdLog.Ldate|stdLog.Ltime|stdLog.Lmicroseconds)
-		logger.level = logVerboseLabel
+	verboseLogger = newLoggerPlus(func(l *loggerPlus) {
+		l.logger = newJSONLogger(io.Discard)
+		l.level = levelVerb
 	})
-	debugLogger = newLoggerPlus(func(logger *loggerPlus) {
-		logger.logger = stdLog.New(os.Stdout, "", stdLog.Ldate|stdLog.Ltime|stdLog.Lmicroseconds)
-		logger.level = logDebugLabel
+	debugLogger = newLoggerPlus(func(l *loggerPlus) {
+		l.logger = newJSONLogger(os.Stdout)
+		l.level = levelDebug
 	})
-	warnLogger = newLoggerPlus(func(logger *loggerPlus) {
-		logger.logger = stdLog.New(os.Stderr, "", stdLog.Ldate|stdLog.Ltime|stdLog.Lmicroseconds)
-		logger.level = logWarnLabel
+	warnLogger = newLoggerPlus(func(l *loggerPlus) {
+		l.logger = newJSONLogger(os.Stderr)
+		l.level = levelWarn
 	})
-	errorLogger = newLoggerPlus(func(logger *loggerPlus) {
-		logger.logger = stdLog.New(os.Stderr, "", stdLog.Ldate|stdLog.Ltime|stdLog.Lmicroseconds)
-		logger.level = logErrorLabel
+	errorLogger = newLoggerPlus(func(l *loggerPlus) {
+		l.logger = newJSONLogger(os.Stderr)
+		l.level = levelError
 	})
 }
diff --git a/internal/logger/log_test.go b/internal/logger/log_test.go
new file mode 100644
index 000000000..626cb73f2
--- /dev/null
+++ b/internal/logger/log_test.go
@@ -0,0 +1,174 @@
+// Copyright (c) 2026 Winlin
+//
+// SPDX-License-Identifier: MIT
+package logger
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"log/slog"
+	"os"
+	"strings"
+	"testing"
+	"time"
+)
+
+func decodeLine(t *testing.T, line []byte) map[string]any {
+	t.Helper()
+	var m map[string]any
+	if err := json.Unmarshal(bytes.TrimSpace(line), &m); err != nil {
+		t.Fatalf("decode %q: %v", line, err)
+	}
+	return m
+}
+
+func bufLoggerPlus(w io.Writer, level slog.Level) *loggerPlus {
+	return newLoggerPlus(func(l *loggerPlus) {
+		l.logger = newJSONLogger(w)
+		l.level = level
+	})
+}
+
+func TestLevelLabel_Known(t *testing.T) {
+	cases := map[slog.Level]string{
+		levelVerb:  "verb",
+		levelDebug: "debug",
+		levelWarn:  "warn",
+		levelError: "error",
+	}
+	for lvl, want := range cases {
+		if got := levelLabel(lvl); got != want {
+			t.Errorf("levelLabel(%v) = %q, want %q", lvl, got, want)
+		}
+	}
+}
+
+func TestLevelLabel_UnknownFallsBackToString(t *testing.T) {
+	got := levelLabel(slog.Level(99))
+	if got == "" {
+		t.Fatalf("levelLabel(99) returned empty")
+	}
+	if got == "verb" || got == "debug" || got == "warn" || got == "error" {
+		t.Fatalf("levelLabel(99) = %q, want slog.Level.String() form", got)
+	}
+}
+
+func TestPrintf_EmitsAllFields(t *testing.T) {
+	var buf bytes.Buffer
+	lp := bufLoggerPlus(&buf, levelDebug)
+	ctx := withContextID(context.Background(), "abc1234")
+	lp.Printf(ctx, "hello %s %d", "world", 42)
+
+	m := decodeLine(t, buf.Bytes())
+	if m["level"] != "debug" {
+		t.Errorf("level = %v, want debug", m["level"])
+	}
+	if m["msg"] != "hello world 42" {
+		t.Errorf("msg = %v, want %q", m["msg"], "hello world 42")
+	}
+	if m["cid"] != "abc1234" {
+		t.Errorf("cid = %v, want abc1234", m["cid"])
+	}
+	pid, ok := m["pid"].(float64)
+	if !ok || int(pid) != os.Getpid() {
+		t.Errorf("pid = %v, want %d", m["pid"], os.Getpid())
+	}
+	ts, ok := m["time"].(string)
+	if !ok || !strings.HasSuffix(ts, "Z") {
+		t.Errorf("time = %v, want UTC suffix Z", m["time"])
+	}
+	if _, err := time.Parse(time.RFC3339Nano, ts); err != nil {
+		t.Errorf("time %q not RFC3339Nano: %v", ts, err)
+	}
+}
+
+func TestPrintf_OmitsCIDWhenAbsent(t *testing.T) {
+	var buf bytes.Buffer
+	bufLoggerPlus(&buf, levelWarn).Printf(context.Background(), "no cid here")
+
+	m := decodeLine(t, buf.Bytes())
+	if v, present := m["cid"]; present {
+		t.Errorf("cid should be absent, got %v", v)
+	}
+	if m["level"] != "warn" {
+		t.Errorf("level = %v, want warn", m["level"])
+	}
+}
+
+func TestPrintf_AllLevelsMapToLabel(t *testing.T) {
+	cases := []struct {
+		level slog.Level
+		label string
+	}{
+		{levelVerb, "verb"},
+		{levelDebug, "debug"},
+		{levelWarn, "warn"},
+		{levelError, "error"},
+	}
+	for _, tc := range cases {
+		var buf bytes.Buffer
+		bufLoggerPlus(&buf, tc.level).Printf(context.Background(), "hi")
+		m := decodeLine(t, buf.Bytes())
+		if m["level"] != tc.label {
+			t.Errorf("level(%v) rendered as %v, want %q", tc.level, m["level"], tc.label)
+		}
+	}
+}
+
+func TestNewJSONLogger_GroupedAttrsPassThrough(t *testing.T) {
+	var buf bytes.Buffer
+	lg := newJSONLogger(&buf)
+	lg.LogAttrs(context.Background(), levelDebug, "grouped",
+		slog.Group("meta", slog.String("inner", "v")))
+
+	m := decodeLine(t, buf.Bytes())
+	meta, ok := m["meta"].(map[string]any)
+	if !ok {
+		t.Fatalf("meta not an object: %v", m["meta"])
+	}
+	if meta["inner"] != "v" {
+		t.Errorf("meta.inner = %v, want v", meta["inner"])
+	}
+}
+
+func TestPackageWrappers_RouteToRightLogger(t *testing.T) {
+	origV, origD, origW, origE := verboseLogger, debugLogger, warnLogger, errorLogger
+	t.Cleanup(func() {
+		verboseLogger, debugLogger, warnLogger, errorLogger = origV, origD, origW, origE
+	})
+
+	vBuf, dBuf, wBuf, eBuf := &bytes.Buffer{}, &bytes.Buffer{}, &bytes.Buffer{}, &bytes.Buffer{}
+	verboseLogger = bufLoggerPlus(vBuf, levelVerb)
+	debugLogger = bufLoggerPlus(dBuf, levelDebug)
+	warnLogger = bufLoggerPlus(wBuf, levelWarn)
+	errorLogger = bufLoggerPlus(eBuf, levelError)
+
+	ctx := context.Background()
+	Vf(ctx, "v=%d", 1)
+	Df(ctx, "d=%d", 2)
+	Wf(ctx, "w=%d", 3)
+	Ef(ctx, "e=%d", 4)
+
+	checks := []struct {
+		name  string
+		buf   *bytes.Buffer
+		label string
+		msg   string
+	}{
+		{"Vf", vBuf, "verb", "v=1"},
+		{"Df", dBuf, "debug", "d=2"},
+		{"Wf", wBuf, "warn", "w=3"},
+		{"Ef", eBuf, "error", "e=4"},
+	}
+	for _, c := range checks {
+		m := decodeLine(t, c.buf.Bytes())
+		if m["level"] != c.label {
+			t.Errorf("%s level = %v, want %v", c.name, m["level"], c.label)
+		}
+		if m["msg"] != c.msg {
+			t.Errorf("%s msg = %v, want %v", c.name, m["msg"], c.msg)
+		}
+	}
+}