Protocol Buffers descriptor sets (FileDescriptorSet)

protoc --descriptor_set_out=out.desc writes a FileDescriptorSet, a message of the schema descriptor.proto that describes one or more .proto files. Its files are usually named .desc, .binpb or .pb. The explorer reads every field below when the bytes fit the schema and every file’s name ends in .proto; custom options in the options messages’ extension ranges are allowed and shown as raw fields. Field numbers are those of the main branch of Protocol Buffers in November 2026.

FileDescriptorSet

Field	Name	Type	Meaning
1	`file`	repeated FileDescriptorProto	The files.

The message and SourceCodeInfo each reserve extension number 536,000,000.

FileDescriptorProto

Field	Name	Type	Meaning
1	`name`	string	The file’s name, relative to a source root.
2	`package`	string	The package.
3	`dependency`	repeated string	Imported files.
10	`public_dependency`	repeated int32	Indexes of imports that are public.
11	`weak_dependency`	repeated int32	Indexes of imports that are weak.
15	`option_dependency`	repeated string	Imports used only for options.
4	`message_type`	repeated DescriptorProto	Top-level messages.
5	`enum_type`	repeated EnumDescriptorProto	Top-level enums.
6	`service`	repeated ServiceDescriptorProto	Services.
7	`extension`	repeated FieldDescriptorProto	Top-level extensions.
8	`options`	FileOptions	File options.
9	`source_code_info`	SourceCodeInfo	Locations and comments, when kept.
12	`syntax`	string	`proto2`, `proto3`, or `editions` for edition files. Missing means proto2.
14	`edition`	Edition	The edition, for edition files.

Edition values

Value	Name
0	`EDITION_UNKNOWN`
1	`EDITION_1_TEST_ONLY`
2	`EDITION_2_TEST_ONLY`
900	`EDITION_LEGACY`
998	`EDITION_PROTO2`
999	`EDITION_PROTO3`
1000	`EDITION_2023`
1001	`EDITION_2024`
1002	`EDITION_2026`
9999	`EDITION_UNSTABLE`
99997	`EDITION_99997_TEST_ONLY`
99998	`EDITION_99998_TEST_ONLY`
99999	`EDITION_99999_TEST_ONLY`
2147483647	`EDITION_MAX`

DescriptorProto

A message type.

Field	Name	Type	Meaning
1	`name`	string	The name.
2	`field`	repeated FieldDescriptorProto	Fields.
6	`extension`	repeated FieldDescriptorProto	Extensions declared inside it.
3	`nested_type`	repeated DescriptorProto	Nested messages.
4	`enum_type`	repeated EnumDescriptorProto	Nested enums.
5	`extension_range`	repeated ExtensionRange	Numbers open to extensions.
8	`oneof_decl`	repeated OneofDescriptorProto	Oneofs.
7	`options`	MessageOptions	Options.
9	`reserved_range`	repeated ReservedRange	Reserved numbers.
10	`reserved_name`	repeated string	Reserved names.
11	`visibility`	SymbolVisibility	Local or exported.

ExtensionRange: a range of numbers open to extensions
Field	Name	Type	Meaning
1	`start`	int32	First number, inclusive.
2	`end`	int32	Last number, exclusive.
3	`options`	ExtensionRangeOptions	Options.

ReservedRange
Field	Name	Type	Meaning
1	`start`	int32	First number, inclusive.
2	`end`	int32	Last number, exclusive.

ExtensionRangeOptions

Field	Name	Type	Meaning
2	`declaration`	repeated Declaration	Which extension uses which number.
50	`features`	FeatureSet	Edition features.
3	`verification`	VerificationState	`DECLARATION` 0 or `UNVERIFIED` 1.
999	`uninterpreted_option`	repeated UninterpretedOption	Options not yet interpreted.

Declaration: one declared extension
Field	Name	Type	Meaning
1	`number`	int32	The extension’s number.
2	`full_name`	string	Its fully qualified name.
3	`type`	string	Its type.
5	`reserved`	bool	Whether the number is reserved.
6	`repeated`	bool	Whether it is repeated.

FieldDescriptorProto

A field, or an extension when extendee is set.

Field	Name	Type	Meaning
1	`name`	string	The name.
3	`number`	int32	The field number.
4	`label`	Label	`LABEL_OPTIONAL` 1, `LABEL_REQUIRED` 2, `LABEL_REPEATED` 3.
5	`type`	Type	The field’s type.
6	`type_name`	string	The name of a message or enum type.
2	`extendee`	string	For an extension: the message it extends.
7	`default_value`	string	An explicit `[default = …]`, as text.
9	`oneof_index`	int32	Index of the oneof it belongs to.
10	`json_name`	string	Its name in ProtoJSON.
8	`options`	FieldOptions	Options.
17	`proto3_optional`	bool	A proto3 `optional` field.

Type values
Value	Name	Value	Name
1	`TYPE_DOUBLE`	10	`TYPE_GROUP`
2	`TYPE_FLOAT`	11	`TYPE_MESSAGE`
3	`TYPE_INT64`	12	`TYPE_BYTES`
4	`TYPE_UINT64`	13	`TYPE_UINT32`
5	`TYPE_INT32`	14	`TYPE_ENUM`
6	`TYPE_FIXED64`	15	`TYPE_SFIXED32`
7	`TYPE_FIXED32`	16	`TYPE_SFIXED64`
8	`TYPE_BOOL`	17	`TYPE_SINT32`
9	`TYPE_STRING`	18	`TYPE_SINT64`

OneofDescriptorProto

Field	Name	Type	Meaning
1	`name`	string	The name.
2	`options`	OneofOptions	Options.

EnumDescriptorProto and EnumValueDescriptorProto

Field	Name	Type	Meaning
1	`name`	string	The name.
2	`value`	repeated EnumValueDescriptorProto	The values.
3	`options`	EnumOptions	Options.
4	`reserved_range`	repeated EnumReservedRange	Reserved numbers.
5	`reserved_name`	repeated string	Reserved names.
6	`visibility`	SymbolVisibility	Local or exported.

EnumReservedRange: inclusive at both ends
Field	Name	Type	Meaning
1	`start`	int32	First number.
2	`end`	int32	Last number.

EnumValueDescriptorProto
Field	Name	Type	Meaning
1	`name`	string	The name.
2	`number`	int32	The number.
3	`options`	EnumValueOptions	Options.

ServiceDescriptorProto and MethodDescriptorProto

Field	Name	Type	Meaning
1	`name`	string	The name.
2	`method`	repeated MethodDescriptorProto	The methods.
3	`options`	ServiceOptions	Options.

MethodDescriptorProto
Field	Name	Type	Meaning
1	`name`	string	The name.
2	`input_type`	string	The request message.
3	`output_type`	string	The response message.
4	`options`	MethodOptions	Options.
5	`client_streaming`	bool	Whether the client streams.
6	`server_streaming`	bool	Whether the server streams.

FileOptions

Extension ranges: 990 to 998 and 1000 to the maximum. Numbers 38 and 42 are reserved.

Field	Name	Type	Meaning
1	`java_package`	string	The Java package.
8	`java_outer_classname`	string	The Java outer class.
10	`java_multiple_files`	bool	One Java file per class.
20	`java_generate_equals_and_hash`	bool	Deprecated.
27	`java_string_check_utf8`	bool	Check UTF-8 in Java.
9	`optimize_for`	OptimizeMode	`SPEED` 1, `CODE_SIZE` 2, `LITE_RUNTIME` 3.
11	`go_package`	string	The Go package.
16	`cc_generic_services`	bool	Generate C++ service stubs.
17	`java_generic_services`	bool	Generate Java service stubs.
18	`py_generic_services`	bool	Generate Python service stubs.
23	`deprecated`	bool	Deprecated.
31	`cc_enable_arenas`	bool	C++ arena allocation.
36	`objc_class_prefix`	string	Objective-C class prefix.
37	`csharp_namespace`	string	C# namespace.
39	`swift_prefix`	string	Swift prefix.
40	`php_class_prefix`	string	PHP class prefix.
41	`php_namespace`	string	PHP namespace.
44	`php_metadata_namespace`	string	PHP metadata namespace.
45	`ruby_package`	string	Ruby package.
50	`features`	FeatureSet	Edition features.
999	`uninterpreted_option`	repeated UninterpretedOption	Options not yet interpreted.

MessageOptions

Extension ranges: 990 to 998 and 1000 to the maximum. Numbers 4, 5, 6, 8 and 9 are reserved.

Field	Name	Type	Meaning
1	`message_set_wire_format`	bool	Use the MessageSet wire format.
2	`no_standard_descriptor_accessor`	bool	No `descriptor()` accessor.
3	`deprecated`	bool	Deprecated.
7	`map_entry`	bool	The synthetic entry of a map field.
11	`deprecated_legacy_json_field_conflicts`	bool	Allows JSON name conflicts, for old files.
12	`features`	FeatureSet	Edition features.
999	`uninterpreted_option`	repeated UninterpretedOption	Options not yet interpreted.

FieldOptions

Extension ranges: 990 to 998 and 1000 to the maximum. Numbers 4 and 18 are reserved.

Field	Name	Type	Meaning
1	`ctype`	CType	`STRING` 0, `CORD` 1, `STRING_PIECE` 2.
2	`packed`	bool	Packed encoding.
6	`jstype`	JSType	`JS_NORMAL` 0, `JS_STRING` 1, `JS_NUMBER` 2.
5	`lazy`	bool	Parse the message lazily.
15	`unverified_lazy`	bool	Lazily, without verification.
3	`deprecated`	bool	Deprecated.
10	`weak`	bool	Deprecated: a weak reference.
16	`debug_redact`	bool	Redact in debug output.
17	`retention`	OptionRetention	`RETENTION_UNKNOWN` 0, `RETENTION_RUNTIME` 1, `RETENTION_SOURCE` 2.
19	`targets`	repeated OptionTargetType	What an option applies to: `TARGET_TYPE_UNKNOWN` 0, `…_FILE` 1, `…_EXTENSION_RANGE` 2, `…_MESSAGE` 3, `…_FIELD` 4, `…_ONEOF` 5, `…_ENUM` 6, `…_ENUM_ENTRY` 7, `…_SERVICE` 8, `…_METHOD` 9.
20	`edition_defaults`	repeated EditionDefault	Defaults per edition.
21	`features`	FeatureSet	Edition features.
22	`feature_support`	FeatureSupport	The editions a feature is available in.
999	`uninterpreted_option`	repeated UninterpretedOption	Options not yet interpreted.

EditionDefault
Field	Name	Type	Meaning
3	`edition`	Edition	The edition.
2	`value`	string	The default, as text.

FeatureSupport
Field	Name	Type	Meaning
1	`edition_introduced`	Edition	First edition.
2	`edition_deprecated`	Edition	Deprecated from.
3	`deprecation_warning`	string	The warning.
4	`edition_removed`	Edition	Removed from.
5	`removal_error`	string	The error.

OneofOptions, EnumOptions, EnumValueOptions, ServiceOptions, MethodOptions

All five end in extension ranges 990 to 998 and 1000 to the maximum, and have an uninterpreted_option field 999.

Message	Field	Name	Meaning
OneofOptions	1	`features`	FeatureSet.
EnumOptions	2	`allow_alias`	Allows two names for one number.
	3	`deprecated`	Deprecated.
	6	`deprecated_legacy_json_field_conflicts`	Allows JSON name conflicts, for old files.
	7	`features`	FeatureSet. Number 5 is reserved.
EnumValueOptions	1	`deprecated`	Deprecated.
	2	`features`	FeatureSet.
	3	`debug_redact`	Redact in debug output.
	4	`feature_support`	FeatureSupport.
ServiceOptions	34	`features`	FeatureSet.
ServiceOptions	33	`deprecated`	Deprecated.
MethodOptions	33	`deprecated`	Deprecated.
	34	`idempotency_level`	`IDEMPOTENCY_UNKNOWN` 0, `NO_SIDE_EFFECTS` 1, `IDEMPOTENT` 2.
	35	`features`	FeatureSet.

UninterpretedOption

An option as written, before protoc has worked out what it is.

Field	Name	Type	Meaning
2	`name`	repeated NamePart	The option’s name, in parts.
3	`identifier_value`	string	An identifier.
4	`positive_int_value`	uint64	A positive integer.
5	`negative_int_value`	int64	A negative integer.
6	`double_value`	double	A number.
7	`string_value`	bytes	A string.
8	`aggregate_value`	string	A message, as text.

NamePart
Field	Name	Type	Meaning
1	`name_part`	string (required)	The part.
2	`is_extension`	bool (required)	Whether it is an extension name in parentheses.

FeatureSet

Edition features at one level. See Editions and features.

Field	Name	Values
1	`field_presence`	`EXPLICIT` 1, `IMPLICIT` 2, `LEGACY_REQUIRED` 3.
2	`enum_type`	`OPEN` 1, `CLOSED` 2.
3	`repeated_field_encoding`	`PACKED` 1, `EXPANDED` 2.
4	`utf8_validation`	`VERIFY` 2, `NONE` 3 (1 reserved).
5	`message_encoding`	`LENGTH_PREFIXED` 1, `DELIMITED` 2.
6	`json_format`	`ALLOW` 1, `LEGACY_BEST_EFFORT` 2.
7	`enforce_naming_style`	`STYLE2024` 1, `STYLE_LEGACY` 2, `STYLE2026` 3.
8	`default_symbol_visibility`	`EXPORT_ALL` 1, `EXPORT_TOP_LEVEL` 2, `LOCAL_ALL` 3, `STRICT` 4.
9	`enforce_proto_limits`	`LEGACY_NO_EXPLICIT_LIMITS` 1, `PROTO_LIMITS2026` 2.

Each enum’s value 0 is its unknown value, as in FIELD_PRESENCE_UNKNOWN. Number 999 is reserved, and numbers 1000 to 9994, 9995 to 9999 and 10000 are open to extensions. A message FeatureSetDefaults gives each edition’s defaults; it is used by tools, not in descriptor sets.

SourceCodeInfo

Where each element is in the source, kept when protoc is given --include_source_info.

Field	Name	Type	Meaning
1	`location`	repeated Location	The locations.

Location
Field	Name	Type	Meaning
1	`path`	repeated int32, packed	Field numbers and indexes leading to the element.
2	`span`	repeated int32, packed	Start line, start column, end line and end column.
3	`leading_comments`	string	The comment before it.
4	`trailing_comments`	string	The comment after it.
6	`leading_detached_comments`	repeated string	Earlier comments, not attached.

GeneratedCodeInfo

Written beside generated code, not in descriptor sets. Maps generated code back to .proto elements.

Field	Name	Type	Meaning
1	`annotation`	repeated Annotation	The annotations.

Annotation
Field	Name	Type	Meaning
1	`path`	repeated int32, packed	Path to the element.
2	`source_file`	string	The source file.
3	`begin`	int32	Where the code starts.
4	`end`	int32	Where the code ends.
5	`semantic`	Semantic	`NONE` 0, `SET` 1, `ALIAS` 2.

.PB File Format – Descriptor sets