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 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

--file-exts <ext>... Only include files with these extensions (e.g. .py .rs)

sem graph Cross-file entity dependency graph

--entity <name> Show dependencies/dependents for a specific entity

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

--file-exts <ext>... Only include files with these extensions

sem impact Show what breaks if an entity changes

<entity> Name of the entity to analyze

--json Output as JSON

--file-exts <ext>... Only include files with these extensions

sem blame Entity-level blame: who last modified each function/class

<file> File to blame

--json Output as 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	9ms	8ms
Adoption	-	single binary, drop into any Git repo

Benchmarks

Real measurements on the sem repo. 50 runs each via hyperfine -N, median reported. LTO-optimized Rust binary with xxHash64 and cached tree resolution.

sem diff across scenarios

Wall-clock time, no shell overhead. Measured with hyperfine -N --warmup 10 --runs 50 on the sem repo.

Small commit (1 file) 5ms

5ms

Medium commit (5 files) 8ms

8ms

Large commit (13 files) 19ms

19ms

Range (8 commits, 30 files) 24ms

24ms

Full semantic understanding in under 25ms. Scales linearly with file count.

sem diff vs git diff

Same commit (5 files), same repo. sem adds entity-level parsing on top of git's line diff.

git diff (line-level only) 9ms

9ms

sem diff (entity-level) 8ms

8ms

Faster than git diff while adding semantic parsing, rename detection, and structural hashing.

Internal profiler

Built-in instrumentation via sem diff --profile. Shows where time is spent inside the binary.

Small commit (1 file, 8 entities)

git2 open repo

1.2ms

git diff + content

0.9ms

parse + match

1.8ms

format output

0.1ms

Total (wall) 4.9ms

Large commit (13 files, 65 entities)

git2 open repo

1.2ms

git diff + content

3.6ms

parse + match (parallel)

10.8ms

format output

0.2ms

Total (wall) 19.4ms

Range: 8 commits (30 files, 1383 entities)

git2 open repo

1.2ms

git diff + content

3.8ms

parse + match (parallel)

17.2ms

format output

0.4ms

Total (wall) 24.0ms

Flame graph

CPU time breakdown for sem diff --commit (large, 13 files). Hover for details.

git2 repo

git diff + content

tree-sitter parse

entity matching

format output