diff --git a/core.go b/core.go
new file mode 100644
index 00000000..fd2e443d
--- /dev/null
+++ b/core.go
@@ -0,0 +1,58 @@
+package ws
+
+import (
+	"io"
+)
+
+// This is how it is capitalized in the RFC.
+type Opcode int
+
+const (
+	Continuation Opcode = iota
+	Text
+	Binary
+	// 3 - 7 are reserved for further non-control frames.
+	Close = 8
+	Ping
+	Pong
+	// 11-16 are reserved for further control frames.
+)
+
+type Header struct {
+	FIN bool
+
+	RSV1 bool
+	RSV2 bool
+	RSV3 bool
+
+	Opcode Opcode
+
+	// Length is an integer because the RFC mandates the MSB bit cannot be set.
+	// So we cannot send or receive a frame with negative length.
+	Length int64
+
+	Masked bool
+	Mask   [4]byte
+}
+
+func (f *Header) Bytes() []byte {
+	panic("TODO")
+}
+
+func (f *Header) MaskPayload(payload []byte) {
+	panic("TODO")
+}
+
+func ReadHeader(w io.Writer) (Header, error) {
+	panic("TODO")
+}
+
+type StatusCode uint16
+
+const (
+	NormalClosure StatusCode = 1000 + iota
+	GoingAway
+	ProtocolError
+	UnsupportedData
+	// ...
+)
diff --git a/go.mod b/go.mod
new file mode 100644
index 00000000..44649774
--- /dev/null
+++ b/go.mod
@@ -0,0 +1 @@
+module nhooyr.io/ws
diff --git a/go.sum b/go.sum
new file mode 100644
index 00000000..e69de29b
diff --git a/ws.go b/ws.go
new file mode 100644
index 00000000..ee3e9da1
--- /dev/null
+++ b/ws.go
@@ -0,0 +1,24 @@
+package ws
+
+import (
+	"bufio"
+	"io"
+	"net"
+	"net/http"
+)
+
+func Writer(w bufio.Writer, typ Opcode) io.WriteCloser {
+	panic("TODO")
+}
+
+func WriteFrame(w io.Writer, typ Opcode, p []byte) error {
+	panic("TODO")
+}
+
+func ReadFrame(r io.Reader) (typ Opcode, payload io.Reader, err error) {
+	panic("TODO")
+}
+
+func Upgrade(w http.ResponseWriter, r *http.Request) (net.Conn, *bufio.ReadWriter, error) {
+	panic("TODO")
+}