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