diff --git a/zcl/json/structure.go b/zcl/json/structure.go
index a48f6c6..ec748aa 100644
--- a/zcl/json/structure.go
+++ b/zcl/json/structure.go
@@ -25,9 +25,40 @@ type expression struct {
 }
 
 func (b *body) Content(schema *zcl.BodySchema) (*zcl.BodyContent, zcl.Diagnostics) {
-	content, _, diags := b.PartialContent(schema)
+	content, newBody, diags := b.PartialContent(schema)
 
-	// TODO: generate errors for the stuff we didn't use in PartialContent
+	hiddenAttrs := newBody.(*body).hiddenAttrs
+
+	var nameSuggestions []string
+	for _, attrS := range schema.Attributes {
+		if _, ok := hiddenAttrs[attrS.Name]; !ok {
+			// Only suggest an attribute name if we didn't use it already.
+			nameSuggestions = append(nameSuggestions, attrS.Name)
+		}
+	}
+	for _, blockS := range schema.Blocks {
+		// Blocks can appear multiple times, so we'll suggest their type
+		// names regardless of whether they've already been used.
+		nameSuggestions = append(nameSuggestions, blockS.Type)
+	}
+
+	for k, attr := range b.obj.Attrs {
+		if _, ok := hiddenAttrs[k]; !ok {
+			var fixItHint string
+			suggestion := nameSuggestion(k, nameSuggestions)
+			if suggestion != "" {
+				fixItHint = fmt.Sprintf(" Did you mean %q?", suggestion)
+			}
+
+			diags = append(diags, &zcl.Diagnostic{
+				Severity: zcl.DiagError,
+				Summary:  "Extraneous JSON object property",
+				Detail:   fmt.Sprintf("No attribute or block type is named %q.%s", k, fixItHint),
+				Subject:  &attr.NameRange,
+				Context:  attr.Range().Ptr(),
+			})
+		}
+	}
 
 	return content, diags
 }
@@ -61,7 +92,6 @@ func (b *body) PartialContent(schema *zcl.BodySchema) (*zcl.BodyContent, zcl.Bod
 					Subject:  &obj.OpenRange,
 				})
 			}
-			usedNames[attrS.Name] = struct{}{}
 			continue
 		}
 		content.Attributes[attrS.Name] = &zcl.Attribute{
diff --git a/zcl/json/structure_test.go b/zcl/json/structure_test.go
index f993654..622e5f7 100644
--- a/zcl/json/structure_test.go
+++ b/zcl/json/structure_test.go
@@ -527,7 +527,7 @@ func TestBodyPartialContent(t *testing.T) {
 		t.Run(fmt.Sprintf("%02d-%s", i, test.src), func(t *testing.T) {
 			file, diags := Parse([]byte(test.src), "test.json")
 			if len(diags) != 0 {
-				t.Errorf("Parse produced diagnostics: %s", diags)
+				t.Fatalf("Parse produced diagnostics: %s", diags)
 			}
 			got, _, diags := file.Body.PartialContent(test.schema)
 			if len(diags) != test.diagCount {
@@ -543,3 +543,57 @@ func TestBodyPartialContent(t *testing.T) {
 		})
 	}
 }
+
+func TestBodyContent(t *testing.T) {
+	// We test most of the functionality already in TestBodyPartialContent, so
+	// this test focuses on the handling of extraneous attributes.
+	tests := []struct {
+		src       string
+		schema    *zcl.BodySchema
+		diagCount int
+	}{
+		{
+			`{"unknown": true}`,
+			&zcl.BodySchema{},
+			1,
+		},
+		{
+			`{"unknow": true}`,
+			&zcl.BodySchema{
+				Attributes: []zcl.AttributeSchema{
+					{
+						Name: "unknown",
+					},
+				},
+			},
+			1,
+		},
+		{
+			`{"unknow": true, "unnown": true}`,
+			&zcl.BodySchema{
+				Attributes: []zcl.AttributeSchema{
+					{
+						Name: "unknown",
+					},
+				},
+			},
+			2,
+		},
+	}
+
+	for i, test := range tests {
+		t.Run(fmt.Sprintf("%02d-%s", i, test.src), func(t *testing.T) {
+			file, diags := Parse([]byte(test.src), "test.json")
+			if len(diags) != 0 {
+				t.Fatalf("Parse produced diagnostics: %s", diags)
+			}
+			_, diags = file.Body.Content(test.schema)
+			if len(diags) != test.diagCount {
+				t.Errorf("Wrong number of diagnostics %d; want %d", len(diags), test.diagCount)
+				for _, diag := range diags {
+					t.Logf(" - %s", diag)
+				}
+			}
+		})
+	}
+}