diff --git a/proto/authzed/api/validation_test/fuzz_test.go b/proto/authzed/api/validation_test/fuzz_test.go
new file mode 100644
index 0000000..5e5a915
--- /dev/null
+++ b/proto/authzed/api/validation_test/fuzz_test.go
@@ -0,0 +1,222 @@
+package validation_test
+
+import (
+	"testing"
+
+	v1 "github.com/authzed/authzed-go/proto/authzed/api/v1"
+)
+
+// FuzzObjectID tests the extended object ID validation with fuzzing.
+// The v1 object ID regex pattern is: ^(([a-zA-Z0-9/_|\-=+]{1,})|\*)$
+// This fuzz test ensures the validation doesn't panic on arbitrary input.
+func FuzzObjectID(f *testing.F) {
+	// Add seed corpus with known valid and invalid object IDs
+	seeds := []string{
+		// Valid object IDs
+		"a",
+		"1",
+		"a-",
+		"A-A-A",
+		"123e4567-e89b-12d3-a456-426614174000",
+		"authn|someauthnvalue",
+		"authn|",
+		"authn|a-b-c-d-e",
+		"authn|a_b",
+		"--=base64YWZzZGZh-ZHNmZHPwn5iK8J+YivC/fmIrwn5iK==",
+		"-",
+		"*",
+		// Invalid object IDs
+		"",
+		"  ",
+		"a@b.com",
+		"test@example.com",
+		"test*",
+		"*test",
+		"t*t",
+		"test@example.*",
+		"authn|a@b.com",
+		// Edge cases
+		"\x00",
+		"\n",
+		"\t",
+		"foo\x00bar",
+		"\u0394\u0394\u0394\u0394",
+	}
+
+	for _, seed := range seeds {
+		f.Add(seed)
+	}
+
+	f.Fuzz(func(t *testing.T, objectID string) {
+		// Test ObjectReference validation
+		objRef := &v1.ObjectReference{
+			ObjectType: "testtype",
+			ObjectId:   objectID,
+		}
+		// We only care that this doesn't panic - validation result can be either valid or invalid
+		_ = objRef.Validate()
+
+		// Test SubjectReference validation with the object ID
+		subjRef := &v1.SubjectReference{
+			Object: &v1.ObjectReference{
+				ObjectType: "testtype",
+				ObjectId:   objectID,
+			},
+		}
+		_ = subjRef.Validate()
+		_ = subjRef.HandwrittenValidate()
+
+		// Test RelationshipFilter validation
+		filter := &v1.RelationshipFilter{
+			ResourceType:       "testtype",
+			OptionalResourceId: objectID,
+		}
+		_ = filter.Validate()
+		_ = filter.HandwrittenValidate()
+
+		// Test SubjectFilter validation
+		subjectFilter := &v1.SubjectFilter{
+			SubjectType:       "testtype",
+			OptionalSubjectId: objectID,
+		}
+		_ = subjectFilter.Validate()
+		_ = subjectFilter.HandwrittenValidate()
+
+		// Test full Relationship validation
+		rel := &v1.Relationship{
+			Resource: &v1.ObjectReference{
+				ObjectType: "testtype",
+				ObjectId:   objectID,
+			},
+			Relation: "testrelation",
+			Subject: &v1.SubjectReference{
+				Object: &v1.ObjectReference{
+					ObjectType: "testtype",
+					ObjectId:   "testsubject",
+				},
+			},
+		}
+		_ = rel.Validate()
+		_ = rel.HandwrittenValidate()
+	})
+}
+
+// FuzzNamespace tests the namespace/object type validation with fuzzing.
+// The v1 namespace regex pattern is: ^([a-z][a-z0-9_]{1,61}[a-z0-9]/)*[a-z][a-z0-9_]{1,62}[a-z0-9]$
+func FuzzNamespace(f *testing.F) {
+	seeds := []string{
+		// Valid namespaces
+		"foo",
+		"bar",
+		"foo1",
+		"bar1",
+		"foo_bar",
+		"foo/bar",
+		"foo/bar/baz",
+		// Invalid namespaces
+		"",
+		"...",
+		"ab",
+		"Foo1",
+		"foo_bar_",
+		"foo/b",
+		"Foo/bar",
+		// Edge cases
+		"\x00",
+		"\n",
+		"\t",
+		"\u0394\u0394\u0394",
+	}
+
+	for _, seed := range seeds {
+		f.Add(seed)
+	}
+
+	f.Fuzz(func(t *testing.T, namespace string) {
+		objRef := &v1.ObjectReference{
+			ObjectType: namespace,
+			ObjectId:   "testid",
+		}
+		_ = objRef.Validate()
+	})
+}
+
+// FuzzRelation tests the relation name validation with fuzzing.
+// The v1 relation regex pattern is: ^[a-z][a-z0-9_]{1,62}[a-z0-9]$
+func FuzzRelation(f *testing.F) {
+	seeds := []string{
+		// Valid relations
+		"foo",
+		"bar",
+		"foo1",
+		"bar1",
+		"foo_bar",
+		"member",
+		"viewer",
+		"owner",
+		// Invalid relations
+		"",
+		"ab",
+		"Foo1",
+		"foo_bar_",
+		"foo/bar",
+		// Edge cases
+		"\x00",
+		"\n",
+		"\t",
+	}
+
+	for _, seed := range seeds {
+		f.Add(seed)
+	}
+
+	f.Fuzz(func(t *testing.T, relation string) {
+		rel := &v1.Relationship{
+			Resource: &v1.ObjectReference{
+				ObjectType: "testtype",
+				ObjectId:   "testid",
+			},
+			Relation: relation,
+			Subject: &v1.SubjectReference{
+				Object: &v1.ObjectReference{
+					ObjectType: "testtype",
+					ObjectId:   "testsubject",
+				},
+			},
+		}
+		_ = rel.Validate()
+
+		// Also test relation in SubjectReference
+		subjRef := &v1.SubjectReference{
+			Object: &v1.ObjectReference{
+				ObjectType: "testtype",
+				ObjectId:   "testid",
+			},
+			OptionalRelation: relation,
+		}
+		_ = subjRef.Validate()
+	})
+}
+
+// FuzzCaveatName tests the caveat name validation with fuzzing.
+func FuzzCaveatName(f *testing.F) {
+	seeds := []string{
+		"test",
+		"my_caveat",
+		"caveat123",
+		"",
+		"\x00",
+		"\n",
+	}
+
+	for _, seed := range seeds {
+		f.Add(seed)
+	}
+
+	f.Fuzz(func(t *testing.T, caveatName string) {
+		caveat := &v1.ContextualizedCaveat{
+			CaveatName: caveatName,
+		}
+		_ = caveat.Validate()
+	})
+}