Semantic version control built on Git.

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

sem is a semantic version control tool that works on top of Git. It parses your code with tree-sitter, extracts every function, class, and method as an entity, and diffs at the entity level instead of lines. This means you see "function blahh was modified" instead of "lines x-y changed."

It works in any Git repo with no setup.

Install

brew install sem-cli

Or install the npm wrapper into node_modules:

npm install --save-dev @ataraxy-labs/sem

With Bun, trust the package so its postinstall script can download the binary:

bun add -d @ataraxy-labs/sem
bun pm trust @ataraxy-labs/sem

Or build from source (requires Rust):

cargo install --git https://github.com/Ataraxy-Labs/sem 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

Name conflict with GNU Parallel

GNU Parallel ships a sem binary (/usr/bin/sem) as a symlink to parallel. If you have both installed, they'll collide. Run sem --version to check which one you're using.

Quick fixes:

# Option 1: alias in your shell profile (~/.bashrc, ~/.zshrc)
alias sem="$HOME/.cargo/bin/sem"

# Option 2: make sure cargo bin comes first in PATH
export PATH="$HOME/.cargo/bin:$PATH"

# Option 3: if installed via Homebrew
export PATH="$(brew --prefix)/bin:$PATH"

If you installed via npm/bun, the binary lives in node_modules/.bin/sem and is invoked through npx sem or bunx sem, which avoids the conflict entirely.

Commands

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

sem stores its SQLite entity cache outside the repository, under the OS cache directory by default. Set SEM_CACHE_DIR=/path/to/cache to override the cache root; repo-local overrides are ignored so cache files do not dirty the working tree.

sem diff

Entity-level diff with rename detection, structural hashing, and word-level inline highlights.

# 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

# Verbose mode (word-level inline diffs for each entity)
sem diff -v

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

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

# Markdown output (for PRs, reports)
sem diff --format markdown

# 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

sem impact

Cross-file dependency graph shows what breaks if an entity changes.

# Full impact analysis
sem impact authenticateUser

# Direct dependencies only
sem impact authenticateUser --deps

# Direct dependents only
sem impact authenticateUser --dependents

# Affected tests only
sem impact authenticateUser --tests

# JSON output
sem impact authenticateUser --json

# Disambiguate by file
sem impact authenticateUser --file src/auth.ts

# Include generated/build directories that repo-wide scans skip by default
sem impact authenticateUser --no-default-excludes

sem blame

Entity-level blame showing who last modified each function, class, or method.

sem blame src/auth.ts

# JSON output
sem blame src/auth.ts --json

sem log

Track how a single entity evolved through git history.

sem log authenticateUser

# Verbose mode (show content diff between versions)
sem log authenticateUser -v

# Limit commits scanned
sem log authenticateUser --limit 20

# JSON output
sem log authenticateUser --json

sem entities

List all entities under a file or directory path. No path is the same as ..

sem entities

sem entities .

sem entities src/auth.ts

# JSON output
sem entities --json
sem entities src/auth.ts --json

# Include generated/build directories that repo-wide scans skip by default
sem entities --no-default-excludes

sem context

Token-budgeted context for LLMs: the entity, its dependencies, and its dependents, fitted to a strict content token budget. When the target signature itself does not fit, JSON output reports target_omitted: true.

sem context authenticateUser

# Custom token budget
sem context authenticateUser --budget 4000

# JSON output
sem context authenticateUser --json

# Include generated/build directories that repo-wide scans skip by default
sem context authenticateUser --no-default-excludes

Use as default Git diff

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

sem setup

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. Also installs a pre-commit hook that shows entity-level blast radius of staged changes.

To disable and go back to normal git diff:

sem unsetup

What it parses

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

Plus structured data formats:

Everything else falls back to chunk-based diffing.

Custom extensions and extensionless files

For files with non-standard extensions, create a .semrc in your project root:

.xyz = cpp
.j = json
.mypy = python

sem also reads .gitattributes patterns (diff= and linguist-language=) if you already have those set up. .semrc takes priority when both define the same extension.

For files with no extension at all, sem detects the language automatically from content (imports, declarations, shebang lines, vim modelines). This covers 19 languages with no config needed.

How matching works

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.

MCP Server

sem includes an MCP server with 6 tools for AI agents: sem_entities, sem_diff, sem_blame, sem_impact, sem_log, sem_context. These mirror the CLI commands exactly.

{
  "mcpServers": {
    "sem": {
      "command": "sem-mcp"
    }
  }
}

Install the MCP binary:

cd sem/crates
cargo install --path sem-mcp

JSON output

sem diff --format json

{
  "summary": {
    "fileCount": 2,
    "added": 1,
    "modified": 1,
    "deleted": 1,
    "moved": 0,
    "renamed": 0,
    "reordered": 0,
    "binary": 0,
    "orphan": 0,
    "total": 3
  },
  "changes": [
    {
      "entityId": "src/auth.ts::function::validateToken",
      "changeType": "added",
      "entityType": "function",
      "entityName": "validateToken",
      "startLine": 12,
      "endLine": 18,
      "oldStartLine": null,
      "oldEndLine": null,
      "filePath": "src/auth.ts"
    }
  ],
  "binaryChanges": []
}

The named change-type buckets (added, modified, deleted, moved, renamed, reordered) always sum to total. orphan is a cross-cutting metadata count for module-level changes, and those changes are already included in the named change-type buckets.

As a library

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

[dependencies]
sem-core = { git = "https://github.com/Ataraxy-Labs/sem", version = "0.5" }

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

Architecture

• 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

License

MIT OR Apache-2.0