sem — Commands & Details

Commands

Every command supports --format json for machine-readable output.

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, json, plain, or markdown

--file-exts <ext>... Filter by extension (e.g. .py .rs)

-v, --verbose Show inline before/after content

--stdin Read file changes from stdin (no git needed)

sem impact What breaks if this entity changes?

<entity> Name of the entity to analyze

--file <path> Disambiguate when multiple entities share a name

--deps Show direct dependencies only

--dependents Show direct dependents only

--tests Show affected test entities only

--json Output as JSON

--file-exts <ext>... Filter by extension

sem blame Who last modified each function/class

<file> File to blame

--json Output as JSON

sem log Evolution of an entity through git history

<entity> Name of the entity to trace

--file <path> File containing the entity (auto-detected if omitted)

--limit <n> Maximum commits to scan (default: 50)

-v, --verbose Show content diff between versions

--json Output as JSON

sem entities List entities under a file or directory path

[path] File or directory path; defaults to .

--json Output as JSON

sem context Token-budgeted context for an entity (for AI prompts)

<entity> Name of the entity

--file <path> Disambiguate when multiple entities share a name

--budget <n> Token budget (default: 8000)

--json Output as JSON

--file-exts <ext>... Filter by extension

sem setup Replace git diff with sem diff globally

Installs a git diff wrapper so every git diff runs through sem automatically

sem unsetup Restore default git diff behavior

JSON output

Pipe 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"
    }
  ]
}

Entity matching

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

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

Phase 2: Structural hash Same AST structure, different name? Renamed or moved.

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

sem vs git

Feature	git diff	sem diff
Granularity	lines	entities (functions, classes, properties)
Code parsing	no	tree-sitter (21 languages)
Config files	lines	key-path entities
Rename detection	heuristic (file-level)	3-phase (ID + hash + fuzzy)
Machine output	patch format	JSON
Agent accuracy	41.5%	95.9% (benchmark)
Speed	9ms	8ms

Benchmarks

Measured with hyperfine on the sem repo. 50 runs, median reported.

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

sem diff vs git diff

Same commit (5 files), same repo.

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

All supported formats

Format	Extensions	Entities
TypeScript	.ts .tsx .mts .cts	functions, classes, interfaces, types, enums, exports
JavaScript	.js .jsx .mjs .cjs	functions, classes, variables, exports
Python	.py	functions, classes, decorated definitions
Go	.go	functions, methods, types, vars, consts
Rust	.rs	functions, structs, enums, impls, traits, mods, consts
Java	.java	classes, methods, interfaces, enums, fields, constructors
C	.c .h	functions, structs, enums, unions, typedefs
C++	.cpp .cc .hpp	functions, classes, structs, enums, namespaces, templates
C#	.cs	classes, methods, interfaces, enums, structs, properties
Ruby	.rb	methods, classes, modules
PHP	.php	functions, classes, methods, interfaces, traits, enums
Swift	.swift	functions, classes, protocols, structs, enums, properties
Elixir	.ex .exs	modules, functions, macros, guards, protocols
Bash	.sh	functions
HCL/Terraform	.hcl .tf .tfvars	blocks, attributes (qualified names)
Kotlin	.kt .kts	classes, interfaces, objects, functions, properties
Fortran	.f90 .f95 .f	functions, subroutines, modules, programs
Vue	.vue	template/script/style blocks + inner TS/JS entities
XML	.xml .plist .svg .csproj	elements (nested, tag-name identity)
ERB	.erb	blocks, expressions, code tags
Svelte	.svelte .svelte.js .svelte.ts	component blocks, rune modules + inner JS/TS entities
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