CrX

CRX is the file format used by Google Chrome and other Chromium-based browsers to package and distribute extensions and themes. A CRX file is typically identified by the .crx extension and serves as a self-contained package containing the extension’s code, assets, and metadata.

Inside a CRX package, the contents are stored as a ZIP archive that includes the extension’s files (such as manifest.json, HTML, JavaScript, CSS, images) along with a cryptographic signature and the publisher’s public key. The header and structure of CRX files vary by version, but a common feature is that the package is signed to verify the publisher’s identity and to ensure the contents have not been tampered with since packaging.

CRX files are generated when developers package extensions for distribution. They are typically distributed through the Chrome Web Store, where updates are delivered securely, or provided directly by developers for manual installation. For development, Chrome offers a “Load unpacked” option that lets developers load extensions from a folder, bypassing the packaging step, to facilitate testing.

Security and compatibility considerations are central to CRX usage. The manifest.json file within every extension declares required permissions and capabilities, and Chrome enforces review and update mechanisms for store-hosted extensions. Installing CRX files from trusted sources is advisable, as untrusted packages may pose security risks. While CRX packaging is standard in Chrome and other Chromium-based browsers, non-Chromium browsers may handle extension formats differently or not support CRX installations.