git-fission

Split large git commits into atomic pieces using AI
Like nuclear fission — a neutron hits a heavy nucleus and splits it into smaller, more stable fragments.

---

What is git-fission?

git-fission analyzes your git commits and helps you split large, non-atomic commits into smaller, focused pieces. It uses AI to understand the semantic meaning of your changes and suggest logical splits.

Supported LLM Providers:

• Anthropic (direct API)
• OpenAI
• OpenRouter
• AWS Bedrock

A commit is considered atomic if it:

• Does one thing (single logical change)
• Is reasonably small (not too many files/lines)
• Has related changes (files in same area)
• Has a clear, descriptive commit message

Installation

# Clone the repository
git clone https://github.com/dreamyang-liu/git-fission.git
cd git-fission

# Install dependencies
npm install

# Build
npm run build

# Link globally (optional)
npm link
# or
ln -s "$(pwd)/dist/index.js" ~/.local/bin/git-fission

Usage

Check the last unpushed commit

git-fission

Split a commit

# Split a commit into atomic pieces
git-fission --split HEAD

# Preview without executing
git-fission --split HEAD --dry-run

# With custom instruction
git-fission --split HEAD -i "Keep test files in a separate commit"

# Use different providers
git-fission --split HEAD -p anthropic                    # Anthropic (default model)
git-fission --split HEAD -p openai -m gpt-4o             # OpenAI
git-fission --split HEAD -m openrouter:anthropic/claude-3.5-haiku  # OpenRouter

# Use a specific model (Bedrock)
git-fission --split HEAD -m us.anthropic.claude-opus-4-5-20251101-v1:0

How it works

                                              ·
                                         ◦
                                    ·  ◦
                               ◦              ⬤━━━━▶
        ╭─────────╮      ·
        │ ◉  ◉  ◉ │   ◦          ⬤━━━━━━━▶
●━━━━▶  │ ◉  ◉  ◉ │
        │ ◉  ◉  ◉ │   ◦          ⬤━━━━━━━▶
        ╰─────────╯      ·
                               ◦              ⬤━━━━▶
                                    ◦  ·
                                         ◦
                                              ·

                        ⚛  git-fission
                  Split commits into atomic pieces

1. Neutron (your command) hits the nucleus (your large commit)
2. Fission occurs — AI analyzes and splits the diff into logical pieces
3. Fragments fly out — multiple atomic commits are created
4. Chain reaction — cleaner git history!

Example

Before:

abc1234 feat: Add user auth, API endpoints, database models, and tests

After running git-fission --split abc1234:

def5678 feat(auth): Add user authentication middleware
ghi9012 feat(api): Add user CRUD endpoints
jkl3456 feat(db): Add User and Session models
mno7890 test: Add user authentication tests

Options

Option	Description
-v, --verbose	Verbose output
-p, --provider <p>	LLM provider: bedrock, anthropic, openai, openrouter
-m, --model <id>	Model ID (or use provider:model format)
--split <commit>	Split a commit into atomic pieces
--dry-run	Preview split without executing
-i, --instruction	Custom instruction for LLM
-h, --help	Show help

Model Format

You can specify the model in two ways:

# Using --provider and --model separately
git-fission -p anthropic -m claude-3-5-sonnet-20241022

# Using provider:model format (provider prefix)
git-fission -m anthropic:claude-3-5-sonnet-20241022
git-fission -m openai:gpt-4o
git-fission -m openrouter:anthropic/claude-3.5-haiku

Environment Variables

Variable	Description
GIT_FISSION_PROVIDER	Default provider (bedrock, anthropic, openai, openrouter)
GIT_FISSION_MODEL	Default model
ANTHROPIC_API_KEY	API key for Anthropic
OPENAI_API_KEY	API key for OpenAI
OPENROUTER_API_KEY	API key for OpenRouter
AWS_BEARER_TOKEN_BEDROCK	Bearer token for Bedrock API
AWS_REGION	AWS region (default: us-west-2)

Available Models Providers

Anthropic (Direct API)

Model	Description
claude-3-5-haiku-20241022	Default, fast
claude-3-5-sonnet-20241022	Balanced
claude-sonnet-4-20250514	Recommended
claude-opus-4-20250514	Most capable

OpenAI

Model	Description
gpt-5-mini-2025-08-07	fast & cheap
gpt-5.2-2025-12-11	High capability

OpenRouter

Model	Description
anthropic/claude-3.5-haiku	Default
anthropic/claude-3.5-sonnet	Balanced
openai/gpt-4o	OpenAI via OpenRouter

AWS Bedrock

Model	Description
us.anthropic.claude-3-5-haiku-20241022-v1:0	Default
us.anthropic.claude-sonnet-4-20250514-v1:0	Recommended
us.anthropic.claude-opus-4-5-20251101-v1:0	Most capable

Features

• Multi-Provider Support: Works with Anthropic, OpenAI, OpenRouter, and AWS Bedrock
• LLM Analysis: Deep semantic analysis using state-of-the-art language models
• Auto-Split: Automatically split large commits into atomic ones
• Hunk-Level Splitting: Fast & stable, splits at diff hunk boundaries
• Custom Instructions: Guide the LLM with custom splitting rules

How Splitting Works

The tool operates at the hunk level. A hunk is a contiguous block of changes in a diff (the sections starting with @@). The AI analyzes each hunk and classifies them into logical groups.

Original commit with 3 hunks in file.ts:
┌─────────────────────────────────┐
│ @@ -10,5 +10,8 @@  ← Hunk 1    │
│ @@ -50,3 +53,6 @@  ← Hunk 2    │
│ @@ -100,4 +106,4 @@ ← Hunk 3   │
└─────────────────────────────────┘
           ↓ git-fission --split
┌─────────────┐  ┌─────────────┐
│ Commit A    │  │ Commit B    │
│ Hunk 1 + 3  │  │ Hunk 2      │
└─────────────┘  └─────────────┘

Requirements

• Node.js 18+
• Git repository
• API key for your chosen provider:
  • Anthropic: ANTHROPIC_API_KEY
  • OpenAI: OPENAI_API_KEY
  • OpenRouter: OPENROUTER_API_KEY
  • AWS Bedrock: AWS credentials or AWS_BEARER_TOKEN_BEDROCK

License

MIT