opencode-fast-apply

OpenCode plugin for Fast Apply - High-performance code editing with OpenAI-compatible APIs.

Features

• Partial file editing - Only send relevant sections (50-500 lines), not entire files
• Smart context matching - Automatically finds and replaces code sections
• Token efficient - Save 80-98% tokens compared to full-file edits
• Lazy edit markers - Use // ... existing code ... for unchanged sections
• Multi-backend support - LM Studio, Ollama, OpenAI, any OpenAI-compatible endpoint
• Robust XML handling - Safely handles special characters and XML tags in code

Installation

npm install -g opencode-fast-apply

Configure your API endpoint:

# LM Studio (default)
export FAST_APPLY_URL="http://localhost:1234"
export FAST_APPLY_MODEL="fastapply-1.5b"
export FAST_APPLY_API_KEY="optional-api-key"

# Ollama
export FAST_APPLY_URL="http://localhost:11434"
export FAST_APPLY_MODEL="codellama:7b"

# OpenAI
export FAST_APPLY_URL="https://api.openai.com"
export FAST_APPLY_MODEL="gpt-4"
export FAST_APPLY_API_KEY="sk-your-key"

Add to OpenCode config (~/.config/opencode/opencode.json):

{
  "plugin": ["opencode-fast-apply"]
}

Restart OpenCode. The fast_apply_edit tool is now available.

Usage

// 1. Read relevant section (not entire file)
const content = await read("src/app.ts", { offset: 100, limit: 50 })

// 2. Edit with partial context
fast_apply_edit({
  target_filepath: "src/app.ts",
  original_code: content,  // Just 50 lines!
  code_edit: `// ... existing code ...
function updated() {
  return "modified";
}
// ... existing code ...`
})

Key points:

• Provide 50-500 lines of context around the area you want to change
• Include 2-5 lines before/after the target section
• Tool automatically finds and replaces that section in the full file
• No need to send entire file (saves tokens and improves speed)

Configuration

| Variable | Default | Description | |----------|---------|-------------| | FAST_APPLY_API_KEY | optional-api-key | API key (optional for local) | | FAST_APPLY_URL | http://localhost:1234 | API endpoint | | FAST_APPLY_MODEL | fastapply-1.5b | Model name |

How It Works

1. AI reads relevant file section (50-500 lines)
2. AI provides original_code (partial context) and code_edit
3. Tool sends to Fast Apply API for merging
4. Tool finds where original_code appears in full file
5. Tool replaces that section with merged code
6. Tool writes full file back and shows diff

Token Savings

| File Size | Before (Full) | After (Partial) | Savings | |-----------|--------------|-----------------|---------| | 100 lines | 2,500 tokens | 500 tokens | -80% | | 500 lines | 12,500 tokens | 1,000 tokens | -92% | | 1000 lines | 25,000 tokens | 1,500 tokens | -94% | | 5000 lines | 125,000 tokens | 2,000 tokens | -98% |

Troubleshooting

"Cannot locate original_code in file"

• File was modified since you read it - re-read and try again
• Whitespace differs - tool tries normalized matching automatically
• Wrong section provided - verify you extracted the correct lines

API connection issues

curl -X POST http://localhost:1234/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{"model":"fastapply-1.5b","messages":[{"role":"user","content":"test"}]}'

License

MIT