USB (Universal Systems Bridge) is an open-source tool for finding, installing, and moving AI skills and capabilities across different agent runtimes. It addresses two problems: skills and MCP servers are scattered across repositories and configurations, and users often have little way to check what they do before installing them. The project offers a catalog of 529 skills, a command-line interface, and an API, with support for 16 runtime targets. Its installer detects local runtimes and can create native files or portable bundles; users can search the catalog, install individual skills or presets, and verify downloads before running them.
A central feature is the Trust Layer, which adds checks beyond installation. The secscan command statically compares a skill’s stated purpose with capabilities indicated by its instructions and bundled scripts, such as accessing credentials, running processes, or deleting files. It reports evidence with file and line references, assigns verdicts and severity, and can block CI on new medium- or high-severity findings; it never executes the material being scanned. Baselines let teams distinguish new issues from known ones, while vague authority language is advisory rather than a standalone failure. For MCP servers, mcprobe observes startup behavior with operator consent but does not invoke tools. Together, the checks aim to expose mismatches between declared purpose and observable behavior, not to guarantee that a capability is safe.
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