What is the GG file format?
A .gg file is a Google Desktop Gadget package - a self-contained mini-application that ran as a floating widget on the Windows desktop through Google Desktop. The format is a standard ZIP archive (magic bytes PK, 50 4B 03 04) containing HTML, JavaScript, CSS, and an XML manifest that defines the gadget's name, description, version, and entry point.
Inside the ZIP, the manifest (typically main.xml or a .gmanifest file) describes gadget metadata and references the HTML interface files. The gadget UI rendered in an embedded browser context provided by Google Desktop; JavaScript handled logic and CSS controlled styling. Optional image assets and icons are included as additional ZIP entries.
Google Desktop was launched in October 2004 and discontinued on September 14, 2011. All .gg files are legacy artifacts - Google Desktop is no longer available and does not run on modern Windows versions. The ZIP contents can still be inspected and extracted with any standard archive tool such as 7-Zip.
The .gg extension has an unrelated second use in the emulation community as a file extension for Sega Game Gear ROM images, which are raw binary dumps with no ZIP signature. The presence or absence of the PK header is the only reliable way to distinguish the two uses.
Security & safety
RISK: LOWAs a ZIP containing HTML/JS, the content is not directly executable on modern Windows without a gadget host (which no longer exists). Historic gadgets from untrusted sources could have contained malicious JavaScript, but this risk is theoretical given no runtime exists. Safe to inspect with a ZIP tool; do not attempt to run via workarounds.
Format details
in a nutshell- Sega Game Gear ROM - Emulators (Kega Fusion, RetroArch, Mesen) use .gg for Sega Game Gear cartridge ROM images - entirely unrelated to Google.
- GeoGebra file (alternative) - Some older GeoGebra installations used .gg; current format is .ggb.
Programs that open GG files
Windows1 app
7-Zip (inspect contents only)
Open-source Rename .gg to .zip, then right-click > Open archive to inspect the HTML/JS/XML contents. The gadget cannot be run. Technical details
deep spec| Container format | ZIP archive (PKZIP); magic bytes PK (50 4B 03 04) at offset 0 |
| Compression | DEFLATE per-entry ZIP compression for text and asset files |
| Encoding | Binary ZIP container; internal content is UTF-8 text (HTML, JavaScript, CSS, XML) |
| Manifest file | main.xml or .gmanifest XML file defining gadget name, description, author, version, and entry HTML |
| UI technology | HTML + JavaScript + CSS rendered in an embedded browser context within Google Desktop |
| Typical file size | 5 KB - 2 MB |
| ZIP integrity | CRC32 checksum per ZIP entry |
| ZIP entry limit | Up to 65,535 entries (standard ZIP central directory limit) |
| Associated OS | Windows only (Google Desktop was Windows-exclusive) |
| Host application status | Google Desktop discontinued September 14, 2011; no functional host application exists |
| Extension collision | .gg is also used for Sega Game Gear ROM files (raw binary; no ZIP/PK signature) |
| Released | 2004 (Google Desktop 1.0) |
| Latest version | N/A - format frozen; Google Desktop discontinued September 14, 2011 |
GG conversions
Community Q&A
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