diff --git a/cerror/code.go b/cerror/code.go
new file mode 100644
index 0000000..ac0fa48
--- /dev/null
+++ b/cerror/code.go
@@ -0,0 +1,36 @@
+package cerror
+
+import (
+	"git.twelvetwelve.org/library/core/log"
+)
+
+var codes = make(map[string]*Code)
+
+type Code struct {
+	code string
+}
+
+func (c *Code) Error() string {
+	return c.code
+}
+
+func NewCode(urn string) *Code {
+	if _, ok := codes[urn]; ok {
+		log.Panicf("error code %s already exists", urn)
+	}
+
+	code := &Code{
+		code: urn,
+	}
+	codes[urn] = code
+	return code
+}
+
+func GetCode(urn string) *Code {
+	if code, ok := codes[urn]; ok {
+		return code
+	}
+
+	log.Panicf("error code %s does not exist", urn)
+	return nil
+}
diff --git a/cerror/error.go b/cerror/error.go
new file mode 100644
index 0000000..8e63c90
--- /dev/null
+++ b/cerror/error.go
@@ -0,0 +1,33 @@
+package cerror
+
+import (
+	"fmt"
+)
+
+type Error struct {
+	code *Code
+	msg  string
+	kv   map[string]interface{}
+}
+
+func (e *Error) Code() *Code {
+	return e.code
+}
+
+func (e *Error) Error() string {
+	return fmt.Sprintf("%s:%s", e.code, e.msg)
+}
+
+func (e *Error) KV(k string, v interface{}) {
+	e.kv[k] = v
+}
+
+func New(code *Code, message string) *Error {
+	e := &Error{
+		code: code,
+		msg:  message,
+		kv:   make(map[string]interface{}),
+	}
+
+	return e
+}
diff --git a/cerror/error_test.go b/cerror/error_test.go
new file mode 100644
index 0000000..2fa8f01
--- /dev/null
+++ b/cerror/error_test.go
@@ -0,0 +1,23 @@
+package cerror
+
+import (
+	"testing"
+
+	"git.twelvetwelve.org/library/core/testutil/assert"
+)
+
+func TestError_Errors(t *testing.T) {
+	c := NewCode("org.twelvetwelve.one")
+	assert.NotNil(t, c)
+
+	e := New(c, "something went wrong")
+	assert.NotNil(t, e)
+
+	assert.Equal(t, e.Code(), c)
+	assert.WillPanic(t, func() { _ = NewCode("org.twelvetwelve.one") })
+	assert.WillPanic(t, func() { _ = GetCode("org.twelvetwelve.two") })
+
+	c2 := NewCode("org.twelvetwelve.two")
+	assert.NotNil(t, c2)
+	assert.NotEqual(t, c, c2)
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..9748bfb
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module git.twelvetwelve.org/library/core
+
+go 1.20
diff --git a/log/default.go b/log/default.go
new file mode 100644
index 0000000..e707712
--- /dev/null
+++ b/log/default.go
@@ -0,0 +1,42 @@
+package log
+
+var Default = &Log{
+	fmtTime: "2006-01-02 15:04:05",
+	level:   LogAll,
+}
+
+func Printf(s string, v ...interface{}) {
+	Default.Printf(s, v...)
+}
+
+func Panicf(s string, v ...interface{}) {
+	Default.Panicf(s, v...)
+}
+
+func Fatalf(s string, v ...interface{}) {
+	Default.Fatalf(s, v...)
+}
+
+func Infof(s string, v ...interface{}) {
+	Default.Infof(s, v...)
+}
+
+func Eventf(s string, v ...interface{}) {
+	Default.Eventf(s, v...)
+}
+
+func Warnf(s string, v ...interface{}) {
+	Default.Warnf(s, v...)
+}
+
+func Debugf(s string, v ...interface{}) {
+	Default.Debugf(s, v...)
+}
+
+func Highlightf(s string, v ...interface{}) {
+	Default.Highlightf(s, v...)
+}
+
+func Errorf(s string, v ...interface{}) {
+	Default.Errorf(s, v...)
+}
diff --git a/log/interface.go b/log/interface.go
new file mode 100644
index 0000000..d56590c
--- /dev/null
+++ b/log/interface.go
@@ -0,0 +1,13 @@
+package log
+
+type Logger interface {
+	Printf(s string, v ...interface{})
+	Panicf(s string, v ...interface{})
+	Fatalf(s string, v ...interface{})
+	Infof(s string, v ...interface{})
+	Eventf(s string, v ...interface{})
+	Warnf(s string, v ...interface{})
+	Debugf(s string, v ...interface{})
+	Highlightf(s string, v ...interface{})
+	Errorf(s string, v ...interface{})
+}
diff --git a/log/log.go b/log/log.go
new file mode 100644
index 0000000..6aff37a
--- /dev/null
+++ b/log/log.go
@@ -0,0 +1,97 @@
+package log
+
+import (
+	"fmt"
+	"os"
+	"time"
+)
+
+const (
+	ColorReset  = "\033[0m"
+	ColorRed    = "\033[31m"
+	ColorGreen  = "\033[32m"
+	ColorYellow = "\033[33m"
+	ColorCyan   = "\033[36m"
+	ColorGray   = "\033[2;37m"
+)
+
+const (
+	LogError = 1 << iota
+	LogWarn
+	LogEvent
+	LogInfo
+	LogHighlight
+	LogPrint
+	LogDebug
+
+	LogAll = LogError | LogWarn | LogEvent | LogInfo | LogHighlight | LogPrint | LogDebug
+)
+
+type Log struct {
+	fmtTime string
+	level   uint32
+}
+
+func (l *Log) Printf(s string, v ...interface{}) {
+	if l.level&LogPrint == LogPrint {
+		l.ColorPrint(ColorGray, fmt.Sprintf(s, v...))
+	}
+}
+
+func (l *Log) Panicf(s string, v ...interface{}) {
+	panic(fmt.Sprintf(s, v...))
+}
+
+func (l *Log) Fatalf(s string, v ...interface{}) {
+	l.ColorPrint(ColorRed, fmt.Sprintf(s, v...))
+	os.Exit(1)
+}
+
+func (l *Log) Infof(s string, v ...interface{}) {
+	if l.level&LogInfo == LogInfo {
+		l.ColorPrint(ColorReset, fmt.Sprintf(s, v...))
+	}
+}
+
+func (l *Log) Eventf(s string, v ...interface{}) {
+	if l.level&LogEvent == LogEvent {
+		l.ColorPrint(ColorCyan, fmt.Sprintf(s, v...))
+	}
+}
+
+func (l *Log) Warnf(s string, v ...interface{}) {
+	if l.level&LogWarn == LogWarn {
+		l.ColorPrint(ColorYellow, fmt.Sprintf(s, v...))
+	}
+}
+
+func (l *Log) Debugf(s string, v ...interface{}) {
+	if l.level&LogDebug == LogDebug {
+		l.ColorPrint(ColorGray, fmt.Sprintf(s, v...))
+	}
+}
+
+func (l *Log) Highlightf(s string, v ...interface{}) {
+	if l.level&LogHighlight == LogHighlight {
+		l.ColorPrint(ColorGreen, fmt.Sprintf(s, v...))
+	}
+}
+
+func (l *Log) Errorf(s string, v ...interface{}) {
+	if l.level&LogHighlight == LogHighlight {
+		l.ColorPrint(ColorRed, fmt.Sprintf(s, v...))
+	}
+}
+
+func (l *Log) ColorPrint(color string, s string) {
+	now := time.Now() // get this early.
+	fmt.Fprintf(os.Stdout, "%s | %s%s%s", now.Format(l.fmtTime), color, s, ColorReset)
+}
+
+func (l *Log) SetLevel(level uint32) {
+	l.level = level
+}
+
+func (l *Log) SetTimeFormat(fmt string) {
+	l.fmtTime = fmt
+}
diff --git a/testutil/assert/asserts.go b/testutil/assert/asserts.go
new file mode 100644
index 0000000..72e6800
--- /dev/null
+++ b/testutil/assert/asserts.go
@@ -0,0 +1,30 @@
+package assert
+
+import (
+	"testing"
+)
+
+func WillPanic(t *testing.T, f func()) {
+	t.Helper()
+	defer func() { _ = recover() }()
+	f()
+	t.Fatalf("should have panicked")
+}
+
+func Equal(t *testing.T, expect, check interface{}) {
+	if expect != check {
+		t.Fatalf("%v:%v not equal", expect, check)
+	}
+}
+
+func NotEqual(t *testing.T, expect, check interface{}) {
+	if expect == check {
+		t.Fatalf("%v:%v equal", expect, check)
+	}
+}
+
+func NotNil(t *testing.T, v interface{}) {
+	if v == nil {
+		t.Fatalf("nil")
+	}
+}