diff --git a/tsweb/log.go b/tsweb/log.go
new file mode 100644
index 000000000..dbb9e7b8f
--- /dev/null
+++ b/tsweb/log.go
@@ -0,0 +1,56 @@
+package tsweb
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// Msg is a structured event log entry.
+type Msg struct {
+	Where    string        `json:"where"`
+	When     time.Time     `json:"when"`
+	Duration time.Duration `json:"duration,omitempty"`
+	Domain   string        `json:"domain,omitempty"`
+	Msg      string        `json:"msg,omitempty"`
+	Err      error         `json:"err,omitempty"`
+	HTTP     *MsgHTTP      `json:"http,omitempty"`
+	Data     interface{}   `json:"data,omitempty"`
+}
+
+// MsgHTTP contains information about the processing of one HTTP
+// request.
+type MsgHTTP struct {
+	Code       int    `json:"code"`
+	Path       string `json:"path"`
+	RemoteAddr string `json:"remote_addr"`
+	UserAgent  string `json:"user_agent"`
+	Referer    string `json:"referer"`
+}
+
+// String returns m as a JSON string.
+func (m Msg) String() string {
+	if m.When.IsZero() {
+		m.When = time.Now()
+	}
+	var buf strings.Builder
+	json.NewEncoder(&buf).Encode(m)
+	ret := buf.String()
+	return ret[:len(ret)-1] // remove trailing newline
+}
+
+// HTTPError is an error with embedded HTTP response information.
+type HTTPError struct {
+	Code int
+	Msg  string // sent to the end-user
+	Err  error
+}
+
+// Error implements the error interface.
+func (e HTTPError) Error() string { return fmt.Sprintf("httperror{%d, %q, %v}", e.Code, e.Msg, e.Err) }
+
+// Error returns an HTTPError containing the given information.
+func Error(code int, msg string, err error) HTTPError {
+	return HTTPError{Code: code, Msg: msg, Err: err}
+}