diff --git a/additional.go b/additional.go
index 121f46e..f8f5133 100644
--- a/additional.go
+++ b/additional.go
@@ -2,6 +2,16 @@ package chioas
 
 import "github.com/go-andiamo/chioas/yaml"
 
+// AdditionalOasProperties is a type (map) of additional OAS properties that can be used for
+// use on any .Additional property
+type AdditionalOasProperties map[string]any
+
+func (ap AdditionalOasProperties) Write(on any, w yaml.Writer) {
+	for k, v := range ap {
+		w.WriteTagValue(k, v)
+	}
+}
+
 // Additional is an interface that can be supplied to many parts of the definition
 // to write additional yaml to the OAS
 type Additional interface {
diff --git a/additional_test.go b/additional_test.go
new file mode 100644
index 0000000..3c0ef79
--- /dev/null
+++ b/additional_test.go
@@ -0,0 +1,29 @@
+package chioas
+
+import (
+	"github.com/go-andiamo/chioas/yaml"
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestWriteAdditional(t *testing.T) {
+	ap := AdditionalOasProperties{"foo": "bar"}
+	w := yaml.NewWriter(nil)
+	writeAdditional(ap, nil, w)
+	data, err := w.Bytes()
+	assert.NoError(t, err)
+	const expect = `foo: bar
+`
+	assert.Equal(t, expect, string(data))
+}
+
+func TestAdditionalOasProperties(t *testing.T) {
+	ap := AdditionalOasProperties{"foo": "bar"}
+	w := yaml.NewWriter(nil)
+	ap.Write(nil, w)
+	data, err := w.Bytes()
+	assert.NoError(t, err)
+	const expect = `foo: bar
+`
+	assert.Equal(t, expect, string(data))
+}
diff --git a/schema.go b/schema.go
index 8a74ef4..afb4ef6 100644
--- a/schema.go
+++ b/schema.go
@@ -51,6 +51,8 @@ type Schema struct {
 	//
 	// Should be one of "string", "object", "array", "boolean", "integer", "number" or "null"
 	Type string
+	// Format is the OAS format
+	Format string
 	// RequiredProperties is the ordered collection of required properties
 	//
 	// If any of the items in Properties is also denoted as Property.Required, these are
@@ -111,7 +113,8 @@ func (s *Schema) writeYaml(withName bool, w yaml.Writer) {
 		writeSchemaRef(s.SchemaRef, s.Type == tagValueTypeArray, w)
 	} else {
 		w.WriteTagValue(tagNameDescription, s.Description).
-			WriteTagValue(tagNameType, defValue(s.Type, tagValueTypeObject))
+			WriteTagValue(tagNameType, defValue(s.Type, tagValueTypeObject)).
+			WriteTagValue(tagNameFormat, s.Format)
 		if s.Ofs != nil {
 			s.Ofs.writeYaml(w)
 		}
@@ -150,8 +153,9 @@ func (s *Schema) writeYaml(withName bool, w yaml.Writer) {
 }
 
 func (s *Schema) writeOfYaml(w yaml.Writer) {
-	w.WriteItemStart(tagNameType, defValue(s.Type, tagValueTypeObject)).
-		WriteTagValue(tagNameDescription, s.Description)
+	w.WriteTagValue(tagNameDescription, s.Description).
+		WriteItemStart(tagNameType, defValue(s.Type, tagValueTypeObject)).
+		WriteTagValue(tagNameFormat, s.Format)
 	if reqs, has := s.getRequiredProperties(); has {
 		w.WriteTagStart(tagNameRequired)
 		for _, rp := range reqs {
diff --git a/schema_test.go b/schema_test.go
index 1b3fde5..208af15 100644
--- a/schema_test.go
+++ b/schema_test.go
@@ -240,6 +240,15 @@ properties:
   oneOf:
     - $ref: "#/components/schemas/foo"
     - $ref: "#/components/schemas/bar"
+`,
+		},
+		{
+			schema: Schema{
+				Type:   "string",
+				Format: "uuid",
+			},
+			expect: `type: string
+format: uuid
 `,
 		},
 	}