undiffstand

AI-assisted diff understanding for human reviewers.

undiffstand is a read-only desktop app that helps human reviewers understand local Git changes with AI.

Features

• Register and reopen local Git repositories
• Review the current working tree against HEAD by default
• Choose the comparison base and target from recent branches, recent commits, and the working tree
• Compare local branches, remote branches, and commit SHAs directly
• Inspect file statistics and Split/Unified diffs
• Explain a changed file's likely intent, risk, concerns, and evidence with the local Codex CLI
• Persist project metadata with Tauri Store
• Check for desktop app updates and install available releases in place

Requirements

• Node.js LTS
• pnpm
• Rust stable
• Git available on PATH
• Codex CLI available on PATH and authenticated with codex login (for AI features)
• Tauri 2 platform prerequisites

Development

pnpm install
pnpm tauri dev

The frontend can also be opened independently with pnpm dev. Outside Tauri it uses deterministic in-memory demo data so the Review flow can be tested without filesystem access or a Codex CLI invocation.

AI configuration

Install and authenticate Codex CLI before launching undiffstand:

codex login
pnpm tauri dev

undiffstand runs codex exec --ephemeral --sandbox read-only in an isolated temporary directory and reuses the CLI's saved authentication, model, and local configuration. This avoids loading repository-specific agent instructions into the analysis process. OPENAI_API_KEY and CODEX_API_KEY are removed from the Codex child process so undiffstand does not use API-key authentication. The selected file diff is provided only when an AI explanation is requested.

Validation

pnpm check
pnpm test
cargo test --manifest-path src-tauri/Cargo.toml
pnpm build
pnpm tauri build

Architecture

• Svelte 5/SvelteKit owns presentation and transient UI state.
• Typed, purpose-specific Tauri commands form the IPC boundary.
• Rust services handle Git CLI calls, project persistence, and Codex CLI execution.
• @git-diff-view/svelte is isolated behind a diff viewer component.
• Git commands run without a shell.

undiffstand does not apply patches, modify repository files, or change Git state.

Diff selection

The review toolbar uses two endpoints: From and To.

• HEAD → working tree is the default and reviews all uncommitted changes
• main → working tree includes committed and uncommitted changes since main
• main → feature compares the tips of two branches directly
• Any two listed commits can be compared directly

The current selection is stored in the page URL so a review can be reopened with the same range.