diff --git a/cache/tiered.go b/cache/tiered.go
index e538c93..6411012 100644
--- a/cache/tiered.go
+++ b/cache/tiered.go
@@ -1,6 +1,10 @@
 package cache
 
-import "reflect"
+import (
+	"reflect"
+
+	"git.sdf.org/jchenry/x"
+)
 
 type tieredCache[K comparable, V any] struct {
 	inner Interface[K, V]
@@ -8,6 +12,8 @@ type tieredCache[K comparable, V any] struct {
 }
 
 func NewTieredCache[K comparable, V any](inner, outer Interface[K, V]) Interface[K, V] {
+	x.Assert(inner != nil, "cache.NewTieredCache: inner cannot be nil")
+	x.Assert(outer != nil, "cache.NewTieredCache: outer cannot be nil")
 	return &tieredCache[K, V]{
 		inner: inner,
 		outer: outer,
diff --git a/database/actor.go b/database/actor.go
index ab7f6dc..dad527d 100644
--- a/database/actor.go
+++ b/database/actor.go
@@ -3,6 +3,8 @@ package database
 import (
 	"context"
 	"database/sql"
+
+	"git.sdf.org/jchenry/x"
 )
 
 type Func func(db *sql.DB)
@@ -13,6 +15,7 @@ type Actor struct {
 }
 
 func (a *Actor) Run(ctx context.Context) error {
+	x.Assert(ctx != nil, "Actor.Run: context cannot be nil")
 	for {
 		select {
 		case f := <-a.ActionChan:
diff --git a/net/http/auth.go b/net/http/auth.go
index 7068ef8..5bae5fa 100644
--- a/net/http/auth.go
+++ b/net/http/auth.go
@@ -6,9 +6,13 @@ import (
 	"fmt"
 	"net/http"
 	"strings"
+
+	"git.sdf.org/jchenry/x"
 )
 
 func BasicAuth(h http.Handler, htpasswd map[string]string, realm string) http.HandlerFunc {
+	x.Assert(len(htpasswd) > 0, "http.BasicAuth: htpassword cannot be empty")
+	x.Assert(len(realm) > 0, "http.BasicAuth: realm cannot be empty")
 	rlm := fmt.Sprintf(`Basic realm="%s"`, realm)
 	sha1 := func(password string) string {
 		s := sha1.New()
diff --git a/pkg.go b/pkg.go
index 51bb964..9d22d90 100644
--- a/pkg.go
+++ b/pkg.go
@@ -9,3 +9,31 @@ func Assert(cond bool, msg string) {
 		panic(errors.New(msg))
 	}
 }
+
+func Check(cond bool, err error) *invariants {
+	return new(invariants).Check(cond, err)
+}
+
+type invariants struct {
+	errs []error
+}
+
+func (i *invariants) Check(cond bool, err error) *invariants {
+	if !cond {
+		i.errs = append(i.errs, err)
+	}
+	return i
+}
+
+func (i *invariants) Join() error {
+	return errors.Join(i.errs...)
+}
+func (i *invariants) First() error {
+	if len(i.errs) > 0 {
+		return i.errs[0]
+	}
+	return nil
+}
+func (i *invariants) All() []error {
+	return i.errs
+}