Microsoft Type Library

File Format
Name	Microsoft Type Library
Ontology	Electronic File Formats Development Microsoft Type Library
Extension(s)	.tlb

Microsoft Type Library (TLB) files store metadata on COM (Component Object Model) APIs (interfaces, methods, data types, etc).

There are two main formats:

• the "original format" – file starts with the bytes "SLTG". PRONOM format 1601. Additionally, the string "TYPELIB" occurs near the end of the file.
• the "new format" – file starts with the bytes "MSFT", normally followed by the bytes 02,00,01,00 (which might be a version number) PRONOM format 1602

(PRONOM claims the TLB format is due to Borland, but that appears to be an error.)

Additionally, you will also find .TLB files which are actually in Windows PE format, and have a type library embedded as a resource. Rarely you may even encounter .TLB files for 16-bit Windows OLE which have a type library resource inside NE format.

The MSFT format is generated by the Windows CreateTypeLib2 API. Conversely, the older SLTG format is generated by the Windows CreateTypeLib API.

Links

• MSFT format reverse-engineered documentation. The original of that document is posted here, but that version displays incorrectly due to a character encoding issue.