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SDTally wiki

SDTally explains what makes up System Data in macOS Storage settings by measuring it, never estimating. It is read-only: it never deletes, never moves anything to the Trash and never uses the network.

It has two parts: the sdtally command-line tool (Rust), which does all the measuring, and SDTally.app (SwiftUI), which runs sdtally and shows the results.

Start here

• Installation: the GitHub Releases disk image, or from source
• First run and permissions: Full Disk Access, the administrator password, Passwordless Root
• Automatic vs Full measurement: the two ways the app measures

Understand the numbers

• Understanding System Data: what System Data is, how macOS storage is laid out, and the measurement pitfalls SDTally avoids
• FAQ: numbers that differ from Finder, space that does not come back, and more

Use the CLI and the data

• CLI reference: every mode and option
• JSON output: the JSON schema in English, including MCP for AI agents

Trust

• Privacy and safety: what SDTally will never do, and how that is enforced
• Passwordless Root helper: the security model of the optional root helper and its known limits

Develop

• Building from source
• Releasing

Repository: https://github.com/guiselig/sdtally · License: GPL-3.0-or-later · Author: Guilherme Selig