diff --git a/internal/jsonschema/schema.go b/internal/jsonschema/schema.go
index af1dbc2..fdc8baf 100644
--- a/internal/jsonschema/schema.go
+++ b/internal/jsonschema/schema.go
@@ -11,11 +11,31 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"iter"
 )
 
 // A Schema is a JSON schema object.
-// It corresponds to the 2020-12 draft, as described in
-// https://json-schema.org/draft/2020-12.
+// It corresponds to the 2020-12 draft, as described in https://json-schema.org/draft/2020-12,
+// specifically:
+// - https://json-schema.org/draft/2020-12/draft-bhutton-json-schema-01
+// - https://json-schema.org/draft/2020-12/draft-bhutton-json-schema-validation-01
+//
+// A Schema value may have non-zero values for more than one field:
+// all relevant non-zero fields are used for validation.
+// There is one exception to provide more Go type-safety: the Type and Types fields
+// are mutually exclusive.
+//
+// Since this struct is a Go representation of a JSON value, it inherits JSON's
+// distinction between nil and empty. Nil slices and maps are considered absent,
+// but empty ones are present and affect validation. For example,
+//
+//	Schema{Enum: nil}
+//
+// is equivalent to an empty schema, so it validates every instance. But
+//
+//	Schema{Enum: []any{}}
+//
+// requires equality to some slice element, so it vacuously rejects every instance.
 type Schema struct {
 	// core
 	ID      string             `json:"$id,omitempty"`
@@ -23,7 +43,7 @@ type Schema struct {
 	Ref     string             `json:"$ref,omitempty"`
 	Comment string             `json:"$comment,omitempty"`
 	Defs    map[string]*Schema `json:"$defs,omitempty"`
-	// definitions is deprecated but still allowed. It is a synonym for defs.
+	// definitions is deprecated but still allowed. It is a synonym for $defs.
 	Definitions map[string]*Schema `json:"definitions,omitempty"`
 
 	Anchor        string          `json:"$anchor,omitempty"`
@@ -192,3 +212,52 @@ func (s *Schema) UnmarshalJSON(data []byte) error {
 
 // Ptr returns a pointer to a new variable whose value is x.
 func Ptr[T any](x T) *T { return &x }
+
+// every applies f preorder to every schema under s including s.
+// It stops when f returns false.
+func (s *Schema) every(f func(*Schema) bool) bool {
+	return s == nil ||
+		f(s) && s.everyChild(f)
+}
+
+// everyChild returns an iterator over the immediate child schemas of s.
+//
+// It does not yield nils from fields holding individual schemas, like Contains,
+// because a nil value indicates that the field is absent.
+// It does yield nils when they occur in slices and maps, so those invalid values
+// can be detected when the schema is validated.
+func (s *Schema) everyChild(f func(*Schema) bool) bool {
+	// Fields that contain individual schemas. A nil is valid: it just means the field isn't present.
+	for _, c := range []*Schema{
+		s.Items, s.AdditionalItems, s.Contains, s.PropertyNames, s.AdditionalProperties,
+		s.If, s.Then, s.Else, s.Not, s.UnevaluatedItems, s.UnevaluatedProperties,
+	} {
+		if c != nil && !f(c) {
+			return false
+		}
+	}
+	// Fields that contain slices of schemas. Yield nils so we can check for their presence.
+	for _, sl := range [][]*Schema{s.PrefixItems, s.AllOf, s.AnyOf, s.OneOf} {
+		for _, c := range sl {
+			if !f(c) {
+				return false
+			}
+		}
+	}
+	// Fields that are maps of schemas. Ditto about nils.
+	for _, m := range []map[string]*Schema{
+		s.Defs, s.Definitions, s.Properties, s.PatternProperties, s.DependentSchemas,
+	} {
+		for _, c := range m {
+			if !f(c) {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// all wraps every in an iterator.
+func (s *Schema) all() iter.Seq[*Schema] {
+	return func(yield func(*Schema) bool) { s.every(yield) }
+}
diff --git a/internal/jsonschema/testdata/draft2020-12/allOf.json b/internal/jsonschema/testdata/draft2020-12/allOf.json
new file mode 100644
index 0000000..9e87903
--- /dev/null
+++ b/internal/jsonschema/testdata/draft2020-12/allOf.json
@@ -0,0 +1,312 @@
+[
+    {
+        "description": "allOf",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                {
+                    "properties": {
+                        "bar": {"type": "integer"}
+                    },
+                    "required": ["bar"]
+                },
+                {
+                    "properties": {
+                        "foo": {"type": "string"}
+                    },
+                    "required": ["foo"]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "allOf",
+                "data": {"foo": "baz", "bar": 2},
+                "valid": true
+            },
+            {
+                "description": "mismatch second",
+                "data": {"foo": "baz"},
+                "valid": false
+            },
+            {
+                "description": "mismatch first",
+                "data": {"bar": 2},
+                "valid": false
+            },
+            {
+                "description": "wrong type",
+                "data": {"foo": "baz", "bar": "quux"},
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allOf with base schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "properties": {"bar": {"type": "integer"}},
+            "required": ["bar"],
+            "allOf" : [
+                {
+                    "properties": {
+                        "foo": {"type": "string"}
+                    },
+                    "required": ["foo"]
+                },
+                {
+                    "properties": {
+                        "baz": {"type": "null"}
+                    },
+                    "required": ["baz"]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "valid",
+                "data": {"foo": "quux", "bar": 2, "baz": null},
+                "valid": true
+            },
+            {
+                "description": "mismatch base schema",
+                "data": {"foo": "quux", "baz": null},
+                "valid": false
+            },
+            {
+                "description": "mismatch first allOf",
+                "data": {"bar": 2, "baz": null},
+                "valid": false
+            },
+            {
+                "description": "mismatch second allOf",
+                "data": {"foo": "quux", "bar": 2},
+                "valid": false
+            },
+            {
+                "description": "mismatch both",
+                "data": {"bar": 2},
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allOf simple types",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                {"maximum": 30},
+                {"minimum": 20}
+            ]
+        },
+        "tests": [
+            {
+                "description": "valid",
+                "data": 25,
+                "valid": true
+            },
+            {
+                "description": "mismatch one",
+                "data": 35,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allOf with boolean schemas, all true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [true, true]
+        },
+        "tests": [
+            {
+                "description": "any value is valid",
+                "data": "foo",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "allOf with boolean schemas, some false",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [true, false]
+        },
+        "tests": [
+            {
+                "description": "any value is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allOf with boolean schemas, all false",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [false, false]
+        },
+        "tests": [
+            {
+                "description": "any value is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allOf with one empty schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                {}
+            ]
+        },
+        "tests": [
+            {
+                "description": "any data is valid",
+                "data": 1,
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "allOf with two empty schemas",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                {},
+                {}
+            ]
+        },
+        "tests": [
+            {
+                "description": "any data is valid",
+                "data": 1,
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "allOf with the first empty schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                {},
+                { "type": "number" }
+            ]
+        },
+        "tests": [
+            {
+                "description": "number is valid",
+                "data": 1,
+                "valid": true
+            },
+            {
+                "description": "string is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allOf with the last empty schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                { "type": "number" },
+                {}
+            ]
+        },
+        "tests": [
+            {
+                "description": "number is valid",
+                "data": 1,
+                "valid": true
+            },
+            {
+                "description": "string is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "nested allOf, to check validation semantics",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                {
+                    "allOf": [
+                        {
+                            "type": "null"
+                        }
+                    ]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "null is valid",
+                "data": null,
+                "valid": true
+            },
+            {
+                "description": "anything non-null is invalid",
+                "data": 123,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allOf combined with anyOf, oneOf",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [ { "multipleOf": 2 } ],
+            "anyOf": [ { "multipleOf": 3 } ],
+            "oneOf": [ { "multipleOf": 5 } ]
+        },
+        "tests": [
+            {
+                "description": "allOf: false, anyOf: false, oneOf: false",
+                "data": 1,
+                "valid": false
+            },
+            {
+                "description": "allOf: false, anyOf: false, oneOf: true",
+                "data": 5,
+                "valid": false
+            },
+            {
+                "description": "allOf: false, anyOf: true, oneOf: false",
+                "data": 3,
+                "valid": false
+            },
+            {
+                "description": "allOf: false, anyOf: true, oneOf: true",
+                "data": 15,
+                "valid": false
+            },
+            {
+                "description": "allOf: true, anyOf: false, oneOf: false",
+                "data": 2,
+                "valid": false
+            },
+            {
+                "description": "allOf: true, anyOf: false, oneOf: true",
+                "data": 10,
+                "valid": false
+            },
+            {
+                "description": "allOf: true, anyOf: true, oneOf: false",
+                "data": 6,
+                "valid": false
+            },
+            {
+                "description": "allOf: true, anyOf: true, oneOf: true",
+                "data": 30,
+                "valid": true
+            }
+        ]
+    }
+]
diff --git a/internal/jsonschema/testdata/draft2020-12/anyOf.json b/internal/jsonschema/testdata/draft2020-12/anyOf.json
new file mode 100644
index 0000000..89b192d
--- /dev/null
+++ b/internal/jsonschema/testdata/draft2020-12/anyOf.json
@@ -0,0 +1,203 @@
+[
+    {
+        "description": "anyOf",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "anyOf": [
+                {
+                    "type": "integer"
+                },
+                {
+                    "minimum": 2
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "first anyOf valid",
+                "data": 1,
+                "valid": true
+            },
+            {
+                "description": "second anyOf valid",
+                "data": 2.5,
+                "valid": true
+            },
+            {
+                "description": "both anyOf valid",
+                "data": 3,
+                "valid": true
+            },
+            {
+                "description": "neither anyOf valid",
+                "data": 1.5,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "anyOf with base schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "type": "string",
+            "anyOf" : [
+                {
+                    "maxLength": 2
+                },
+                {
+                    "minLength": 4
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "mismatch base schema",
+                "data": 3,
+                "valid": false
+            },
+            {
+                "description": "one anyOf valid",
+                "data": "foobar",
+                "valid": true
+            },
+            {
+                "description": "both anyOf invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "anyOf with boolean schemas, all true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "anyOf": [true, true]
+        },
+        "tests": [
+            {
+                "description": "any value is valid",
+                "data": "foo",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "anyOf with boolean schemas, some true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "anyOf": [true, false]
+        },
+        "tests": [
+            {
+                "description": "any value is valid",
+                "data": "foo",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "anyOf with boolean schemas, all false",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "anyOf": [false, false]
+        },
+        "tests": [
+            {
+                "description": "any value is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "anyOf complex types",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "anyOf": [
+                {
+                    "properties": {
+                        "bar": {"type": "integer"}
+                    },
+                    "required": ["bar"]
+                },
+                {
+                    "properties": {
+                        "foo": {"type": "string"}
+                    },
+                    "required": ["foo"]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "first anyOf valid (complex)",
+                "data": {"bar": 2},
+                "valid": true
+            },
+            {
+                "description": "second anyOf valid (complex)",
+                "data": {"foo": "baz"},
+                "valid": true
+            },
+            {
+                "description": "both anyOf valid (complex)",
+                "data": {"foo": "baz", "bar": 2},
+                "valid": true
+            },
+            {
+                "description": "neither anyOf valid (complex)",
+                "data": {"foo": 2, "bar": "quux"},
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "anyOf with one empty schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "anyOf": [
+                { "type": "number" },
+                {}
+            ]
+        },
+        "tests": [
+            {
+                "description": "string is valid",
+                "data": "foo",
+                "valid": true
+            },
+            {
+                "description": "number is valid",
+                "data": 123,
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "nested anyOf, to check validation semantics",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "anyOf": [
+                {
+                    "anyOf": [
+                        {
+                            "type": "null"
+                        }
+                    ]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "null is valid",
+                "data": null,
+                "valid": true
+            },
+            {
+                "description": "anything non-null is invalid",
+                "data": 123,
+                "valid": false
+            }
+        ]
+    }
+]
diff --git a/internal/jsonschema/testdata/draft2020-12/if-then-else.json b/internal/jsonschema/testdata/draft2020-12/if-then-else.json
new file mode 100644
index 0000000..1c35d7e
--- /dev/null
+++ b/internal/jsonschema/testdata/draft2020-12/if-then-else.json
@@ -0,0 +1,268 @@
+[
+    {
+        "description": "ignore if without then or else",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "if": {
+                "const": 0
+            }
+        },
+        "tests": [
+            {
+                "description": "valid when valid against lone if",
+                "data": 0,
+                "valid": true
+            },
+            {
+                "description": "valid when invalid against lone if",
+                "data": "hello",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "ignore then without if",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "then": {
+                "const": 0
+            }
+        },
+        "tests": [
+            {
+                "description": "valid when valid against lone then",
+                "data": 0,
+                "valid": true
+            },
+            {
+                "description": "valid when invalid against lone then",
+                "data": "hello",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "ignore else without if",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "else": {
+                "const": 0
+            }
+        },
+        "tests": [
+            {
+                "description": "valid when valid against lone else",
+                "data": 0,
+                "valid": true
+            },
+            {
+                "description": "valid when invalid against lone else",
+                "data": "hello",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "if and then without else",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "if": {
+                "exclusiveMaximum": 0
+            },
+            "then": {
+                "minimum": -10
+            }
+        },
+        "tests": [
+            {
+                "description": "valid through then",
+                "data": -1,
+                "valid": true
+            },
+            {
+                "description": "invalid through then",
+                "data": -100,
+                "valid": false
+            },
+            {
+                "description": "valid when if test fails",
+                "data": 3,
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "if and else without then",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "if": {
+                "exclusiveMaximum": 0
+            },
+            "else": {
+                "multipleOf": 2
+            }
+        },
+        "tests": [
+            {
+                "description": "valid when if test passes",
+                "data": -1,
+                "valid": true
+            },
+            {
+                "description": "valid through else",
+                "data": 4,
+                "valid": true
+            },
+            {
+                "description": "invalid through else",
+                "data": 3,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "validate against correct branch, then vs else",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "if": {
+                "exclusiveMaximum": 0
+            },
+            "then": {
+                "minimum": -10
+            },
+            "else": {
+                "multipleOf": 2
+            }
+        },
+        "tests": [
+            {
+                "description": "valid through then",
+                "data": -1,
+                "valid": true
+            },
+            {
+                "description": "invalid through then",
+                "data": -100,
+                "valid": false
+            },
+            {
+                "description": "valid through else",
+                "data": 4,
+                "valid": true
+            },
+            {
+                "description": "invalid through else",
+                "data": 3,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "non-interference across combined schemas",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "allOf": [
+                {
+                    "if": {
+                        "exclusiveMaximum": 0
+                    }
+                },
+                {
+                    "then": {
+                        "minimum": -10
+                    }
+                },
+                {
+                    "else": {
+                        "multipleOf": 2
+                    }
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "valid, but would have been invalid through then",
+                "data": -100,
+                "valid": true
+            },
+            {
+                "description": "valid, but would have been invalid through else",
+                "data": 3,
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "if with boolean schema true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "if": true,
+            "then": { "const": "then" },
+            "else": { "const": "else" }
+        },
+        "tests": [
+            {
+                "description": "boolean schema true in if always chooses the then path (valid)",
+                "data": "then",
+                "valid": true
+            },
+            {
+                "description": "boolean schema true in if always chooses the then path (invalid)",
+                "data": "else",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "if with boolean schema false",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "if": false,
+            "then": { "const": "then" },
+            "else": { "const": "else" }
+        },
+        "tests": [
+            {
+                "description": "boolean schema false in if always chooses the else path (invalid)",
+                "data": "then",
+                "valid": false
+            },
+            {
+                "description": "boolean schema false in if always chooses the else path (valid)",
+                "data": "else",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "if appears at the end when serialized (keyword processing sequence)",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "then": { "const": "yes" },
+            "else": { "const": "other" },
+            "if": { "maxLength": 4 }
+        },
+        "tests": [
+            {
+                "description": "yes redirects to then and passes",
+                "data": "yes",
+                "valid": true
+            },
+            {
+                "description": "other redirects to else and passes",
+                "data": "other",
+                "valid": true
+            },
+            {
+                "description": "no redirects to then and fails",
+                "data": "no",
+                "valid": false
+            },
+            {
+                "description": "invalid redirects to else and fails",
+                "data": "invalid",
+                "valid": false
+            }
+        ]
+    }
+]
diff --git a/internal/jsonschema/testdata/draft2020-12/not.json b/internal/jsonschema/testdata/draft2020-12/not.json
new file mode 100644
index 0000000..346d4a7
--- /dev/null
+++ b/internal/jsonschema/testdata/draft2020-12/not.json
@@ -0,0 +1,301 @@
+[
+    {
+        "description": "not",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": {"type": "integer"}
+        },
+        "tests": [
+            {
+                "description": "allowed",
+                "data": "foo",
+                "valid": true
+            },
+            {
+                "description": "disallowed",
+                "data": 1,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "not multiple types",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": {"type": ["integer", "boolean"]}
+        },
+        "tests": [
+            {
+                "description": "valid",
+                "data": "foo",
+                "valid": true
+            },
+            {
+                "description": "mismatch",
+                "data": 1,
+                "valid": false
+            },
+            {
+                "description": "other mismatch",
+                "data": true,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "not more complex schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": {
+                "type": "object",
+                "properties": {
+                    "foo": {
+                        "type": "string"
+                    }
+                }
+             }
+        },
+        "tests": [
+            {
+                "description": "match",
+                "data": 1,
+                "valid": true
+            },
+            {
+                "description": "other match",
+                "data": {"foo": 1},
+                "valid": true
+            },
+            {
+                "description": "mismatch",
+                "data": {"foo": "bar"},
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "forbidden property",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "properties": {
+                "foo": {
+                    "not": {}
+                }
+            }
+        },
+        "tests": [
+            {
+                "description": "property present",
+                "data": {"foo": 1, "bar": 2},
+                "valid": false
+            },
+            {
+                "description": "property absent",
+                "data": {"bar": 1, "baz": 2},
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "forbid everything with empty schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": {}
+        },
+        "tests": [
+            {
+                "description": "number is invalid",
+                "data": 1,
+                "valid": false
+            },
+            {
+                "description": "string is invalid",
+                "data": "foo",
+                "valid": false
+            },
+            {
+                "description": "boolean true is invalid",
+                "data": true,
+                "valid": false
+            },
+            {
+                "description": "boolean false is invalid",
+                "data": false,
+                "valid": false
+            },
+            {
+                "description": "null is invalid",
+                "data": null,
+                "valid": false
+            },
+            {
+                "description": "object is invalid",
+                "data": {"foo": "bar"},
+                "valid": false
+            },
+            {
+                "description": "empty object is invalid",
+                "data": {},
+                "valid": false
+            },
+            {
+                "description": "array is invalid",
+                "data": ["foo"],
+                "valid": false
+            },
+            {
+                "description": "empty array is invalid",
+                "data": [],
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "forbid everything with boolean schema true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": true
+        },
+        "tests": [
+            {
+                "description": "number is invalid",
+                "data": 1,
+                "valid": false
+            },
+            {
+                "description": "string is invalid",
+                "data": "foo",
+                "valid": false
+            },
+            {
+                "description": "boolean true is invalid",
+                "data": true,
+                "valid": false
+            },
+            {
+                "description": "boolean false is invalid",
+                "data": false,
+                "valid": false
+            },
+            {
+                "description": "null is invalid",
+                "data": null,
+                "valid": false
+            },
+            {
+                "description": "object is invalid",
+                "data": {"foo": "bar"},
+                "valid": false
+            },
+            {
+                "description": "empty object is invalid",
+                "data": {},
+                "valid": false
+            },
+            {
+                "description": "array is invalid",
+                "data": ["foo"],
+                "valid": false
+            },
+            {
+                "description": "empty array is invalid",
+                "data": [],
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "allow everything with boolean schema false",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": false
+        },
+        "tests": [
+            {
+                "description": "number is valid",
+                "data": 1,
+                "valid": true
+            },
+            {
+                "description": "string is valid",
+                "data": "foo",
+                "valid": true
+            },
+            {
+                "description": "boolean true is valid",
+                "data": true,
+                "valid": true
+            },
+            {
+                "description": "boolean false is valid",
+                "data": false,
+                "valid": true
+            },
+            {
+                "description": "null is valid",
+                "data": null,
+                "valid": true
+            },
+            {
+                "description": "object is valid",
+                "data": {"foo": "bar"},
+                "valid": true
+            },
+            {
+                "description": "empty object is valid",
+                "data": {},
+                "valid": true
+            },
+            {
+                "description": "array is valid",
+                "data": ["foo"],
+                "valid": true
+            },
+            {
+                "description": "empty array is valid",
+                "data": [],
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "double negation",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": { "not": {} }
+        },
+        "tests": [
+            {
+                "description": "any value is valid",
+                "data": "foo",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "collect annotations inside a 'not', even if collection is disabled",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "not": {
+                "$comment": "this subschema must still produce annotations internally, even though the 'not' will ultimately discard them",
+                "anyOf": [
+                    true,
+                    { "properties": { "foo": true } }
+                ],
+                "unevaluatedProperties": false
+            }
+        },
+        "tests": [
+            {
+                "description": "unevaluated property",
+                "data": { "bar": 1 },
+                "valid": true
+            },
+            {
+                "description": "annotations are still collected inside a 'not'",
+                "data": { "foo": 1 },
+                "valid": false
+            }
+        ]
+     }
+]
diff --git a/internal/jsonschema/testdata/draft2020-12/oneOf.json b/internal/jsonschema/testdata/draft2020-12/oneOf.json
new file mode 100644
index 0000000..7a7c7ff
--- /dev/null
+++ b/internal/jsonschema/testdata/draft2020-12/oneOf.json
@@ -0,0 +1,293 @@
+[
+    {
+        "description": "oneOf",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [
+                {
+                    "type": "integer"
+                },
+                {
+                    "minimum": 2
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "first oneOf valid",
+                "data": 1,
+                "valid": true
+            },
+            {
+                "description": "second oneOf valid",
+                "data": 2.5,
+                "valid": true
+            },
+            {
+                "description": "both oneOf valid",
+                "data": 3,
+                "valid": false
+            },
+            {
+                "description": "neither oneOf valid",
+                "data": 1.5,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf with base schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "type": "string",
+            "oneOf" : [
+                {
+                    "minLength": 2
+                },
+                {
+                    "maxLength": 4
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "mismatch base schema",
+                "data": 3,
+                "valid": false
+            },
+            {
+                "description": "one oneOf valid",
+                "data": "foobar",
+                "valid": true
+            },
+            {
+                "description": "both oneOf valid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf with boolean schemas, all true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [true, true, true]
+        },
+        "tests": [
+            {
+                "description": "any value is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf with boolean schemas, one true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [true, false, false]
+        },
+        "tests": [
+            {
+                "description": "any value is valid",
+                "data": "foo",
+                "valid": true
+            }
+        ]
+    },
+    {
+        "description": "oneOf with boolean schemas, more than one true",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [true, true, false]
+        },
+        "tests": [
+            {
+                "description": "any value is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf with boolean schemas, all false",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [false, false, false]
+        },
+        "tests": [
+            {
+                "description": "any value is invalid",
+                "data": "foo",
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf complex types",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [
+                {
+                    "properties": {
+                        "bar": {"type": "integer"}
+                    },
+                    "required": ["bar"]
+                },
+                {
+                    "properties": {
+                        "foo": {"type": "string"}
+                    },
+                    "required": ["foo"]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "first oneOf valid (complex)",
+                "data": {"bar": 2},
+                "valid": true
+            },
+            {
+                "description": "second oneOf valid (complex)",
+                "data": {"foo": "baz"},
+                "valid": true
+            },
+            {
+                "description": "both oneOf valid (complex)",
+                "data": {"foo": "baz", "bar": 2},
+                "valid": false
+            },
+            {
+                "description": "neither oneOf valid (complex)",
+                "data": {"foo": 2, "bar": "quux"},
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf with empty schema",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [
+                { "type": "number" },
+                {}
+            ]
+        },
+        "tests": [
+            {
+                "description": "one valid - valid",
+                "data": "foo",
+                "valid": true
+            },
+            {
+                "description": "both valid - invalid",
+                "data": 123,
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf with required",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "type": "object",
+            "oneOf": [
+                { "required": ["foo", "bar"] },
+                { "required": ["foo", "baz"] }
+            ]
+        },
+        "tests": [
+            {
+                "description": "both invalid - invalid",
+                "data": {"bar": 2},
+                "valid": false
+            },
+            {
+                "description": "first valid - valid",
+                "data": {"foo": 1, "bar": 2},
+                "valid": true
+            },
+            {
+                "description": "second valid - valid",
+                "data": {"foo": 1, "baz": 3},
+                "valid": true
+            },
+            {
+                "description": "both valid - invalid",
+                "data": {"foo": 1, "bar": 2, "baz" : 3},
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "oneOf with missing optional property",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [
+                {
+                    "properties": {
+                        "bar": true,
+                        "baz": true
+                    },
+                    "required": ["bar"]
+                },
+                {
+                    "properties": {
+                        "foo": true
+                    },
+                    "required": ["foo"]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "first oneOf valid",
+                "data": {"bar": 8},
+                "valid": true
+            },
+            {
+                "description": "second oneOf valid",
+                "data": {"foo": "foo"},
+                "valid": true
+            },
+            {
+                "description": "both oneOf valid",
+                "data": {"foo": "foo", "bar": 8},
+                "valid": false
+            },
+            {
+                "description": "neither oneOf valid",
+                "data": {"baz": "quux"},
+                "valid": false
+            }
+        ]
+    },
+    {
+        "description": "nested oneOf, to check validation semantics",
+        "schema": {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "oneOf": [
+                {
+                    "oneOf": [
+                        {
+                            "type": "null"
+                        }
+                    ]
+                }
+            ]
+        },
+        "tests": [
+            {
+                "description": "null is valid",
+                "data": null,
+                "valid": true
+            },
+            {
+                "description": "anything non-null is invalid",
+                "data": 123,
+                "valid": false
+            }
+        ]
+    }
+]
diff --git a/internal/jsonschema/validate.go b/internal/jsonschema/validate.go
index a3baf94..f8743d1 100644
--- a/internal/jsonschema/validate.go
+++ b/internal/jsonschema/validate.go
@@ -166,6 +166,70 @@ func (st *state) validate(instance reflect.Value, schema *Schema, path []any) (e
 		}
 	}
 
+	// logic
+	// https://json-schema.org/draft/2020-12/json-schema-core#section-10.2
+	// These must happen before arrays and objects because if they evaluate an item or property,
+	// then the unevaluatedItems/Properties schemas don't apply to it.
+	// See https://json-schema.org/draft/2020-12/json-schema-core#section-11.2, paragraph 4.
+	//
+	// If any of these fail, then validation fails, even if there is an unevaluatedXXX
+	// keyword in the schema. The spec is unclear about this, but that is the intention.
+
+	valid := func(s *Schema) bool { return st.validate(instance, s, path) == nil }
+
+	if schema.AllOf != nil {
+		for _, ss := range schema.AllOf {
+			if err := st.validate(instance, ss, path); err != nil {
+				return err
+			}
+		}
+	}
+	if schema.AnyOf != nil {
+		ok := false
+		for _, ss := range schema.AnyOf {
+			if valid(ss) {
+				ok = true
+				break
+			}
+		}
+		if !ok {
+			return fmt.Errorf("anyOf: did not validate against any of %v", schema.AnyOf)
+		}
+	}
+	if schema.OneOf != nil {
+		// Exactly one.
+		var okSchema *Schema
+		for _, ss := range schema.OneOf {
+			if valid(ss) {
+				if okSchema != nil {
+					return fmt.Errorf("oneOf: validated against both %v and %v", okSchema, ss)
+				}
+				okSchema = ss
+			}
+		}
+		if okSchema == nil {
+			return fmt.Errorf("oneOf: did not validate against any of %v", schema.OneOf)
+		}
+	}
+	if schema.Not != nil {
+		if valid(schema.Not) {
+			return fmt.Errorf("not: validated against %v", schema.Not)
+		}
+	}
+	if schema.If != nil {
+		var ss *Schema
+		if valid(schema.If) {
+			ss = schema.Then
+		} else {
+			ss = schema.Else
+		}
+		if ss != nil {
+			if err := st.validate(instance, ss, path); err != nil {
+				return err
+			}
+		}
+	}
+
 	return nil
 }
 
diff --git a/internal/jsonschema/validate_test.go b/internal/jsonschema/validate_test.go
index 78e45f8..9baf142 100644
--- a/internal/jsonschema/validate_test.go
+++ b/internal/jsonschema/validate_test.go
@@ -50,8 +50,10 @@ func TestValidate(t *testing.T) {
 				t.Fatal(err)
 			}
 			for _, g := range groups {
-				if g.Schema.Properties != nil {
-					t.Skip("schema has properties")
+				for s := range g.Schema.all() {
+					if s.Properties != nil {
+						t.Skip("schema or subschema has properties")
+					}
 				}
 				rs := &ResolvedSchema{root: g.Schema}
 				t.Run(g.Description, func(t *testing.T) {