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The harness exposes a local tool registry. Each tool is classified as read-only or mutating so permission modes can make reliable decisions. Each entry is a capability in the broader registry — it also declares a group, network usage, scope requirements, and audit behavior. Roles grant capabilities by group, and the full normalized schema lives in the Capabilities reference.

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Tool classes

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MCP tools

MCP servers configured for Claude (~/.claude.json, project .mcp.json) and Codex (~/.codex/config.toml, project .codex/config.toml) are discovered automatically. ~/.config/voss/mcp.yml and project .voss/mcp.yml override imported entries; set enabled: false to turn one off. Stdio and Streamable HTTP servers are supported, and MCP calls go through the same network and permission checks as built-in tools.

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Diff previews

File write tools produce a diff preview before permission decisions. This keeps risky changes inspectable before approval.

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View tools locally

The command shows registered tools and whether each one mutates state.
Tool mutability is data in the registry. Voss should not infer safety from a tool name alone. Inspect the full capability surface with voss capabilities list and voss capabilities inspect <name>.