AnchorCli/docs/HASHLINE.md

The Hashline Technique

Hashline is AnchorCli's unique approach to safe, precise file editing.

How It Works

Every line returned by file tools is prefixed with a content-derived hash anchor:

  function hello() {
    return "world";
  }

The format is lineNumber:hash|content where:

• lineNumber is the current line number in the file
• hash is an Adler-8 checksum derived from the line content and position
• content is the actual line text

Editing with Anchors

When editing, you reference these line:hash anchors instead of reproducing old content. Before any mutation, both the line number and hash are validated — stale anchors are rejected immediately.

Example

To replace lines 2-3 from the example above:

{
  "tool": "replace_lines",
  "path": "example.js",
  "startAnchor": "2:f1",
  "endAnchor": "3:0e",
  "newLines": ["    return \"hello world\";"]
}

Benefits

This eliminates:

• Whitespace/indentation reproduction errors — No need to match exact spacing
• Silent edits to the wrong line — Hash validation ensures you're editing the right content
• Entire-file rewrites — Change just one line without touching the rest
• Line drift in batch operations — BatchEdit validates all anchors upfront and applies changes bottom-to-top

Key Principles

1. Never include anchors in your content — When using replace_lines, insert_after, or similar tools, the newLines parameter should contain raw source code only, WITHOUT the lineNumber:hash| prefix
2. Always validate before editing — Re-read files to get fresh anchors if your previous anchors fail validation
3. Use BatchEdit for multiple changes — This validates all anchors upfront and applies operations atomically

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