open-agent-library/rule/morph-fast-apply.md

description

description
IMPORTANT: Always prefer `morph_edit` over `edit` (string replace) or full file writes when modifying existing files. `morph_edit` works with partial code snippets and does NOT require full file content.

Morph Fast Apply - Tool Selection Guide

When editing code files, choose the appropriate tool based on the situation:

Tool Selection Matrix

Situation	Tool	Reason
Small, exact string replacement	edit	Fast, precise, no API call
Large file (500+ lines)	morph_edit	10x faster, handles partial snippets
Multiple scattered changes	morph_edit	Batch changes efficiently
Complex refactoring	morph_edit	Better accuracy with context
Whitespace-sensitive edits	morph_edit	Forgiving with formatting
New file creation	write	Standard file creation

Using morph_edit

The morph_edit tool uses lazy edit markers to represent unchanged code:

// ... existing code ...
function updatedFunction() {
  // New implementation
  return "modified";
}
// ... existing code ...

Parameters

• target_filepath: Path to the file (relative to project root)
• instructions: Brief description of changes (helps AI disambiguate)
• code_edit: Code with // ... existing code ... markers

Rules

1. ALWAYS use // ... existing code ... for unchanged sections
2. Include minimal context around edits for precise location
3. Preserve exact indentation in your code snippets
4. For deletions: show context before/after, omit the deleted lines
5. Batch multiple edits to the same file in one call

Examples

Adding a function:

// ... existing code ...
import { newDep } from './newDep';
// ... existing code ...

function newFeature() {
  return newDep.process();
}
// ... existing code ...

Modifying existing code:

// ... existing code ...
function existingFunc(param) {
  // Updated implementation
  const result = param * 2; // Changed from * 1
  return result;
}
// ... existing code ...

Deleting code (show what remains):

// ... existing code ...
function keepThis() {
  return "stays";
}

// The function between these two was removed

function alsoKeepThis() {
  return "also stays";
}
// ... existing code ...

Fallback Behavior

If Morph API fails (timeout, rate limit, etc.), the tool will:

1. Return an error message with details
2. Suggest using the native edit tool as fallback
3. The native edit tool requires exact string matching

When NOT to Use morph_edit

• Simple one-line changes (use edit)
• New file creation (use write)
• When you have the exact text to match (use edit for speed)
• When Morph API is unavailable (fall back to edit)