gblorb

GBLORB is a binary container format used in the development and distribution of interactive fiction and text‑based adventure games. It was created in the early 2010s as an extension of the Blorb format, which had become standard for distributing graphical interactive fiction compiled with the Glulx virtual machine. GBLORB adds support for richer metadata, allowing publishers to embed licensing information, resource dependency lists, and platform‑specific assets in a single file. The file extension is typically .gblorb, though older implementations sometimes use .gbi.

The format is structured as a sequence of fixed‑length “boxes.” Each box begins with a four‑byte identifier, followed by a four‑byte length field, and then the payload. Common box types include “PACK” for the main program code, “IMAG” for bitmap graphics, “TUNE” for background music, and “META” for descriptive tags. When a GBLORB is launched by a Glulx interpreter that supports the format, the interpreter first reads the META box to decide which auxiliary assets to load.

Despite its similarity to Blorb, GBLORB is not backward compatible with older Glulx engines. Only newer versions of the Interpretive Fiction Writing System (IFWS) and the Free Adventure Game Engine (FAGE) recognize GBLORB files. Many distribution platforms now include automatic conversion from Blorb to GBLORB as part of their build pipelines, enabling creators to ship games with fewer runtime dependencies.

Technical documentation for the GBLORB specification is available on the IFWS GitHub repository. The format is maintained by the Interactive Fiction Community Association, and the community has produced tools for inspecting, converting, and packaging GBLOB files.