Know what changed.

Entity-level diffs on top of Git. Structured output for AI agents, CI pipelines, and humans who want more than line numbers.

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

or: brew install ataraxy-labs/tap/sem

~/project

$ 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

Commands

--format json for machine-readable output. More commands coming soon.

sem diff Semantic diff of changes

-s, --staged Show staged changes only

-c, --commit <sha> Diff a specific commit

--from <ref> --to <ref> Diff a commit range

-f, --format <fmt> terminal (default) or json

Supported formats

Format	Extensions	Entities
TypeScript	.ts .tsx	functions, classes, interfaces, types, enums
JavaScript	.js .jsx .mjs .cjs	functions, classes, variables
Python	.py	functions, classes, decorators
Go	.go	functions, methods, types
Rust	.rs	functions, structs, enums, impls, traits
JSON	.json	properties, objects (RFC 6901 paths)
YAML	.yml .yaml	sections, properties (dot paths)
TOML	.toml	sections, properties
CSV	.csv .tsv	rows (first column as ID)
Markdown	.md .mdx	heading-based sections

Entity matching

Three-phase algorithm that detects additions, modifications, deletions, renames, and moves.

Phase 1 — Exact ID Same entity ID in before/after? Modified or unchanged.

Phase 2 — Content hash Same SHA-256, different name? Renamed or moved.

Phase 3 — Fuzzy similarity >80% Jaccard token overlap? Probable rename.

Output

Structured JSON. Pipe sem into your AI agent, CI pipeline, or automation.

sem diff --format json | jq

{
  "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 vs git

git gives you lines. sem gives you entities — functions, properties, rows, sections.

Feature	git diff	sem diff
Diff granularity	lines	entities (functions, classes, properties)
Code parsing	no	tree-sitter (TS, Python, Go, Rust, JS)
JSON / YAML / TOML	lines	key-path entities
CSV	lines	row + cell identity
Rename detection	heuristic (file-level)	3-phase (ID + hash + fuzzy)
Machine-readable output	patch format	JSON
Agent accuracy	41.5% avg	95.9% avg (benchmark)
Speed	20ms	30ms
Adoption	-	single binary, drop into any Git repo

Benchmarks

Real measurements on the sem repo. 20 runs each via hyperfine, median reported. Compiled Rust binary with all tree-sitter grammars built in.

sem diff across scenarios

Wall-clock time including process startup. Measured with hyperfine --warmup 3.

Small commit (1 file) 11ms

11ms

Large commit (11 files) 22ms

22ms

Medium commit (7 files, TS + JSON) 30ms

30ms

Range (8 commits, 19 files) 40ms

40ms

Full semantic understanding in under 40ms. Scales linearly with file count.

sem diff vs git diff

git2 repo

git diff + content

tree-sitter parse

entity matching

format output