BYAML (File Format)

For the Mario Kart 8 and Mario Kart 8 Deluxe-specific course BYAML, see course_muunt.byaml (File Format).

BYAML is a generic file format used on Wii U and the Nintendo Switch in games like Mario Kart 8 and Mario Kart 8 Deluxe. BYML is basically the same, and is used in games like Super Mario 3D World and Super Mario Odyssey.

File Format

Header

The file starts with a 0x10 or 0x14 bytes long header. An offset can be 0 meaning it points to nothing.

Offset	Type	Description
0x00	Char[2]	File magic. BY for big endian files, and YB for little endian files.
0x02	UInt16	File format version.
0x04	UInt32	Node name string table node offset.
0x08	UInt32	String value string table node offset..
0x0C	UInt32	Serialized data table node offset. Usually doesn't exist for BYML files.
0x10	UInt32	Root node. Must be an array node or dictionary node.

Nodes

The file consists of multiple nodes, stored in a hierarchy. There are two special-purpose nodes, string table node and serialized data table node, which can only be linked by the header and cannot be stored in the hierarchy of nodes. Only two nodes allow storing children, dictionary node and array node. Each child element consists of a 32-bit integer. If the child node is four bytes long, then the 32-bit integer represents the value of the child node. If the child node is larger than four bytes, then the 32-bit integer represents an absolute offset to the data of the node. For Int32 and Float, the data is stored directly since those are exactly four bytes long, but array node and Int64 are examples where an offset is stored.

The following table shows all available node types:

ID	Name	Available since version
0xA0	String reference	1
0xA1	Serialized data reference	1
0xC0	Array	1
0xC1	Dictionary	1
0xC2	String table	1
0xC3	Serialized data table	1
0xD0	Boolean	1
0xD1	Int32	1
0xD2	Float	1
0xD3	UInt32	2
0xD4	Int64	2 or 3
0xD5	UInt64	2 or 3
0xD6	Double	2
0xFF	Null	2 or 3

Array Node

An array node consists a collection of child nodes, all of arbitrary types. An array node has the following structure:

Offset	Type	Description
0x00	Byte	Node type. Must be 0xC0.
0x01	UInt24	Number of child elements.
0x04	Byte[N]	Child node types. Each byte represents a node type.
Align by 4.

The child elements comes after the structure, altough at an offset aligned by four. If the size of the child node is four bytes, then the direct value is stored. Otherwise a 32-bit offset is stored, which points to the child data. See nodes.

Dictionary Node

A dictionary node consists of a named child nodes. Like an array node, it stores a collection of child nodes, although in a dictionary node all child nodes are named. A dictionary node has the following structure:

Offset	Type	Description
0x00	Byte	Node type. Must be 0xC1.
0x01	UInt24	Number of child elements.

After that, each dictionary entry is stored, each of which describes a child node. It has the following structure:

Offset	Type	Description
0x00	UInt24	Name index. Index of string into the node name string table node linked in the header which represents the name of this node.
0x03	Byte	Child node type. See nodes.
0x04	UInt32	Child element. If the size of the child node is four bytes, then the direct value is stored. Otherwise a 32-bit offset is stored, which points to the child data. See nodes.

Dictionary look-up

When looking up a string in a dictionary node, binary search is done twice. First, binary search is used to find the index of the name into the node name string table node. If the name doesn't exist, then there is no node in the dictionary with that name. However, if it does exist, binary search is used again to find if there is a node with a name index matching the index which was looked up earlier. In order for this to work, the dictionary entries must be sorted on name index.

String Table Node

A string table node stores strings and is accessed by an index in a dictionary node or string node. The node can only be linked in the header. All strings are null-terminated, and must be sorted on true UTF-8 order in order to allow binary search. The node starts with the following structure:

Offset	Type	Description
0x00	Byte	Node type. Must be 0xC2.
0x01	UInt24	Number of strings.
0x04	UInt32[N + 1]	String offsets. The last offset points to the end of the last string. The offsets are relative to the start of this node structure.

Serialized Data Table Node

The serialized data table node stores a collection of generic data. What the data contains is game-specific. Serialized data is accessed by a serialized data node. The node starts with the following structure:

Offset	Type	Description
0x00	Byte	Node type. Must be 0xC3.
0x01	UInt24	Number of serialized data elements.
0x04	UInt32[N + 1]	Serialized data offsets. The last offset points to the end of the last entry. The offsets are relative to the start of this node structure. The size of each entry is known by looking at the next data offset.

Value Nodes

The following table shows all nodes which cannot contain children and are not special-purpose.

ID	Name	Size	Descrption
0xA0	String reference	4	32-bit integer which represents an index into the string value string table linked in the header.
0xA1	Serialized data reference	4	32-bit integer which represents an index into the serialized data table node linked in the header.
0xD0	Boolean	4	32-bit integer boolean, where 1 represents true and 0 represents false.
0xD1	Int32	4	32-bit signed integer.
0xD2	Float	4	32-bit floating-point.
0xD3	UInt32	4	32-bit unsigned integer.
0xD4	Int64	8	64-bit signed integer.
0xD5	UInt64	8	64-bit unsigned integer.
0xD6	Double	8	64-bit floating-point.
0xFF	Null	4	Null. Generally this is used to specify a null value for a string. A 32-bit zero value is stored as a dummy value.

Tools

The following tools can handle BYAML/BYML files:

• (none)