Instead of lines changed, sem tells you what entities changed: functions, methods, classes.

sem diff

┌─ src/auth/login.ts ──────────────────────────────────
│
│  ⊕ function  validateToken          [added]
│  ∆ function  authenticateUser       [modified]
│  ⊖ function  legacyAuth             [deleted]
│
└──────────────────────────────────────────────────────

┌─ config/database.yml ─────────────────────────────────
│
│  ∆ property  production.pool_size   [modified]
│    - 5
│    + 20
│
└──────────────────────────────────────────────────────

Summary: 1 added, 1 modified, 1 deleted across 2 files

brew install sem-cli

Or build from source (requires Rust):

git clone https://github.com/Ataraxy-Labs/sem
cd sem/crates
cargo install --path sem-cli

Or grab a binary from GitHub Releases.

Or run via Docker:

docker build -t sem .
docker run --rm -it -u "$(id -u):$(id -g)" -v "$(pwd):/repo" sem diff

Works in any Git repo. No setup required. Also works outside Git for arbitrary file comparison.

# Semantic diff of working changes
sem diff

# Staged changes only
sem diff --staged

# Specific commit
sem diff --commit abc1234

# Commit range
sem diff --from HEAD~5 --to HEAD

# Plain text output (git status style)
sem diff --format plain

# JSON output (for AI agents, CI pipelines)
sem diff --format json

# Compare any two files (no git repo needed)
sem diff file1.ts file2.ts

# Read file changes from stdin (no git repo needed)
echo '[{"filePath":"src/main.rs","status":"modified","beforeContent":"...","afterContent":"..."}]' \
  | sem diff --stdin --format json

# Only specific file types
sem diff --file-exts .py .rs

# Entity dependency graph
sem graph

# Impact analysis (what breaks if this entity changes?)
sem impact validateToken

# Entity-level blame
sem blame src/auth.ts

Replace git diff output with entity-level diffs. Agents and humans get sem output automatically without changing any commands.

# Set sem as your git diff tool
git config --global diff.external sem-diff-wrapper

# Create the wrapper script
echo '#!/bin/sh
sem diff "$2" "$5"' > ~/.local/bin/sem-diff-wrapper
chmod +x ~/.local/bin/sem-diff-wrapper

Now git diff shows entity-level changes instead of line-level. No prompts, no agent configuration needed. Everything that calls git diff gets sem output automatically.

To disable and go back to normal git diff:

git config --global --unset diff.external

20 programming languages with full entity extraction via tree-sitter:

Plus structured data formats:

Everything else falls back to chunk-based diffing.

Three-phase entity matching:

1. Exact ID match — same entity in before/after = modified or unchanged
2. Structural hash match — same AST structure, different name = renamed or moved (ignores whitespace/comments)
3. Fuzzy similarity — >80% token overlap = probable rename

This means sem detects renames and moves, not just additions and deletions. Structural hashing also distinguishes cosmetic changes (whitespace, formatting) from real logic changes.

sem diff --format json

{
  "summary": {
    "fileCount": 2,
    "added": 1,
    "modified": 1,
    "deleted": 1,
    "total": 3
  },
  "changes": [
    {
      "entityId": "src/auth.ts::function::validateToken",
      "changeType": "added",
      "entityType": "function",
      "entityName": "validateToken",
      "filePath": "src/auth.ts"
    }
  ]
}

sem-core can be used as a Rust library dependency:

[dependencies]
sem-core = { git = "https://github.com/Ataraxy-Labs/sem", version = "0.3" }

Used by weave (semantic merge driver) and inspect (entity-level code review).

• tree-sitter for code parsing (native Rust, not WASM)
• git2 for Git operations
• rayon for parallel file processing
• xxhash for structural hashing
• Plugin system for adding new languages and formats

Want to add a new language? See CONTRIBUTING.md for a step-by-step guide.

MIT OR Apache-2.0