Protocol Buffers well-known types, field by field

The well-known types are the messages that ship with Protocol Buffers in package google.protobuf, in the .proto files under src/google/protobuf (syntax = "proto3"). In the binary format they are ordinary messages: their fields are encoded like any other, and nothing in the bytes marks a message as a Timestamp or an Any. Only ProtoJSON and the generated code give them special forms. The tables give each field’s number, so that their bytes can be read without the schema; the explorer, which has no schema for a plain .pb file, shows them by number. The field lists are those of the protobuf repository’s main branch in November 2026.

Any

any.proto: a message of any type, with the name of its type.

Field	Name	Type	Wire type	Meaning
1	`type_url`	string	LEN	A URL whose last path segment is the message’s full name, usually `type.googleapis.com/` followed by the name, such as `type.googleapis.com/google.protobuf.Duration`.
2	`value`	bytes	LEN	The message, serialised: a message of that type, nested as bytes.

Timestamp

timestamp.proto: a point in time, counted from the Unix epoch (1970-01-01T00:00:00Z) in UTC, ignoring leap seconds.

Field	Name	Type	Wire type	Meaning
1	`seconds`	int64	VARINT	Seconds since the epoch, from -62135596800 (0001-01-01T00:00:00Z) to 253402300799 (9999-12-31T23:59:59Z) inclusive.
2	`nanos`	int32	VARINT	Nanoseconds, from 0 to 999,999,999. Never negative: a time before the epoch with a fraction has negative seconds and nanos that count forward.

One and a half seconds after the epoch, seconds 1 and nanos 500,000,000:

Bytes	Meaning
`08 01`	Field 1, VARINT: `seconds` = 1
`10 80 CA B5 EE 01`	Field 2, VARINT: `nanos` = 500,000,000

Duration

duration.proto: a signed span of time.

Field	Name	Type	Wire type	Meaning
1	`seconds`	int64	VARINT	Seconds, from -315,576,000,000 to +315,576,000,000 inclusive (about ±10,000 years).
2	`nanos`	int32	VARINT	Nanoseconds, from -999,999,999 to +999,999,999. For a span of a second or more, non-zero nanos have the same sign as seconds.

A negative int32 or int64 takes ten bytes as a varint (see Varints), so a negative duration is longer than a positive one.

Struct, Value, ListValue and NullValue

struct.proto: a JSON-like value held in a message.

Struct
Field	Name	Type	Wire type	Meaning
1	`fields`	map<string, Value>	LEN, one per entry	The members, as map entries: key field 1, value field 2.

Value: one oneof, `kind`
Field	Name	Type	Wire type	Meaning
1	`null_value`	NullValue	VARINT	JSON null; the only value is 0.
2	`number_value`	double	I64	A number.
3	`string_value`	string	LEN	A string.
4	`bool_value`	bool	VARINT	true or false.
5	`struct_value`	Struct	LEN	An object.
6	`list_value`	ListValue	LEN	An array.

ListValue
Field	Name	Type	Wire type	Meaning
1	`values`	repeated Value	LEN, one per value	The elements.

NullValue is an enum with one value, NULL_VALUE = 0. Because a oneof member is written even at its default, a null is the two bytes 08 00.

FieldMask

field_mask.proto: a set of field paths, for partial reads and updates.

Field	Name	Type	Wire type	Meaning
1	`paths`	repeated string	LEN, one per path	Paths of field names joined by dots, such as `user.display_name`, in the schema’s names (snake_case).

Wrappers

wrappers.proto: a scalar in a message of its own, to tell an unset value from a zero. Each has one field, value, number 1; an absent field is the default, so a wrapper holding zero is an empty message.

Message	Field 1 type	Wire type
DoubleValue	double	I64
FloatValue	float	I32
Int64Value	int64	VARINT
UInt64Value	uint64	VARINT
Int32Value	int32	VARINT
UInt32Value	uint32	VARINT
BoolValue	bool	VARINT
StringValue	string	LEN
BytesValue	bytes	LEN

Empty

empty.proto: a message with no fields, used as a request or response that carries nothing. Its encoding is zero bytes.

Type, Field, Enum, EnumValue and Option

type.proto: a description of a message or enum type, used by APIs that describe types at run time (and in Api). It is a simpler relative of the descriptor messages.

Type
Field	Name	Type	Meaning
1	`name`	string	The fully qualified message name.
2	`fields`	repeated Field	The fields.
3	`oneofs`	repeated string	The names of the oneofs.
4	`options`	repeated Option	The options.
5	`source_context`	SourceContext	The file it was defined in.
6	`syntax`	Syntax	The syntax of that file.
7	`edition`	string	The edition, when syntax is SYNTAX_EDITIONS.

Field
Field	Name	Type	Meaning
1	`kind`	Field.Kind	The field’s type, below.
2	`cardinality`	Field.Cardinality	0 unknown, 1 optional, 2 required, 3 repeated.
3	`number`	int32	The field number.
4	`name`	string	The field name.
6	`type_url`	string	For a message or enum field, the type’s URL, as in Any.
7	`oneof_index`	int32	1 plus the index of its oneof in `Type.oneofs`; 0 when it is in none.
8	`packed`	bool	Whether a repeated field is packed.
9	`options`	repeated Option	The options.
10	`json_name`	string	The JSON name.
11	`default_value`	string	The default, as text (proto2).

Field 5 is not used. Field.Kind: 0 TYPE_UNKNOWN, 1 TYPE_DOUBLE, 2 TYPE_FLOAT, 3 TYPE_INT64, 4 TYPE_UINT64, 5 TYPE_INT32, 6 TYPE_FIXED64, 7 TYPE_FIXED32, 8 TYPE_BOOL, 9 TYPE_STRING, 10 TYPE_GROUP, 11 TYPE_MESSAGE, 12 TYPE_BYTES, 13 TYPE_UINT32, 14 TYPE_ENUM, 15 TYPE_SFIXED32, 16 TYPE_SFIXED64, 17 TYPE_SINT32, 18 TYPE_SINT64 (the same numbers as FieldDescriptorProto.Type, with 0 added).

Enum
Field	Name	Type	Meaning
1	`name`	string	The fully qualified enum name.
2	`enumvalue`	repeated EnumValue	The values.
3	`options`	repeated Option	The options.
4	`source_context`	SourceContext	The file it was defined in.
5	`syntax`	Syntax	The syntax of that file.
6	`edition`	string	The edition, when syntax is SYNTAX_EDITIONS.

EnumValue and Option
Message	Field	Name	Type
EnumValue	1	`name`	string
EnumValue	2	`number`	int32
EnumValue	3	`options`	repeated Option
Option	1	`name`	string: the option’s name, such as `map_entry` or a custom option’s full name
Option	2	`value`	Any: the value, a wrapper for a scalar or the message itself

Syntax: 0 SYNTAX_PROTO2, 1 SYNTAX_PROTO3, 2 SYNTAX_EDITIONS.

Api, Method and Mixin

api.proto: a description of a service, its methods and the services it includes.

Api
Field	Name	Type	Meaning
1	`name`	string	The fully qualified service name.
2	`methods`	repeated Method	The methods.
3	`options`	repeated Option	The options.
4	`version`	string	The API’s version, such as `v1`.
5	`source_context`	SourceContext	The file it was defined in.
6	`mixins`	repeated Mixin	Services whose methods it includes.
7	`syntax`	Syntax	The syntax of that file.
8	`edition`	string	The edition, when syntax is SYNTAX_EDITIONS.

Method
Field	Name	Type	Meaning
1	`name`	string	The method’s simple name.
2	`request_type_url`	string	The request message’s type URL.
3	`request_streaming`	bool	Whether requests are streamed.
4	`response_type_url`	string	The response message’s type URL.
5	`response_streaming`	bool	Whether responses are streamed.
6	`options`	repeated Option	The options.
7	`syntax`	Syntax	The syntax.
8	`edition`	string	The edition.

Mixin and SourceContext
Message	Field	Name	Type	Meaning
Mixin	1	`name`	string	The included service’s full name.
Mixin	2	`root`	string	A path prefix for the included methods’ HTTP paths.
SourceContext	1	`file_name`	string	The path of the `.proto` file, such as `google/protobuf/source_context.proto` (`source_context.proto`).

.PB File Format – Well-known types

Any