Hashline Edit Server

MCP server providing hashline-based file editing — line-addressed edits with content hashes for integrity verification.

Based on hashline edit format from oh-my-pi.

What is Hashline?

LLM reads file, every line tagged with short content hash:

1:a3|function hello() {
2:f1|  return "world";
3:0e|}

Model references tags when editing — "replace line 2:f1", "replace range 1:a3 through 3:0e", "insert after 3:0e". If file changed since last read, hashes won't match, edit rejected before corruption.

Model doesn't need to reproduce old content/whitespace to identify changes. Benchmarks show hashline matches or beats str_replace for most models, weakest models gain most (up to 10x improvement).

Requirements

• Bun runtime (Bun.hash.xxHash32 for line hashing)
• ripgrep (rg) on PATH for grep tool

Install

npm install mcp-hashline-edit-server
# or
bun add mcp-hashline-edit-server

Usage

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "hashline-edit": {
      "command": "bunx",
      "args": ["mcp-hashline-edit-server"]
    }
  }
}

Cursor

Add to .cursor/mcp.json (project root or global):

{
  "mcpServers": {
    "hashline-edit": {
      "command": "bunx",
      "args": ["mcp-hashline-edit-server"]
    }
  }
}

Any MCP client

Server runs over stdio:

bunx mcp-hashline-edit-server

From source

git clone https://github.com/Submerisble/mcp-hashline-edit-server.git
cd mcp-hashline-edit-server
bun install
bun run src/index.ts

Tools

read_file

Read file with hashline-prefixed output (LINE:HASH|content).

Parameter	Type	Description
path	string	File path (relative or absolute)
offset	number?	Start line (1-indexed)
limit	number?	Max lines (default: 2000)

edit_file

Edit file using hash-verified line references. Four edit variants:

set_line — Replace single line:

{"set_line": {"anchor": "2:f1", "new_text": "  return \"universe\";"}}

replace_lines — Replace range:

{"replace_lines": {"start_anchor": "1:a3", "end_anchor": "3:0e", "new_text": "function greet() {\n  return \"hi\";\n}"}}

insert_after — Insert after line:

{"insert_after": {"anchor": "1:a3", "text": "  // new comment"}}

replace — Fuzzy substring replace (fallback, no hashes needed):

{"replace": {"old_text": "return \"world\"", "new_text": "return \"universe\""}}

Parameter	Type	Description
path	string	File path
edits	array	Edit operations

Edits validated atomically against file as last read. Sorted, applied bottom-up automatically.

write_file

Create or overwrite file.

Parameter	Type	Description
path	string	File path
content	string	Content to write

grep

Search files with hashline-prefixed results.

Parameter	Type	Description
pattern	string	Regex pattern
path	string?	File or directory
glob	string?	Filter by glob (e.g., *.js)
type	string?	Filter by file type
i	boolean?	Case-insensitive
pre	number?	Context lines before
post	number?	Context lines after
limit	number?	Max matches (default: 100)

Requires rg (ripgrep) on system.

How the Hash Works

1. Strip trailing \r
2. Remove all whitespace
3. xxHash32 on whitespace-stripped string
4. Modulo 256, encode as 2-char lowercase hex (00-ff)

Hash whitespace-insensitive — indentation changes don't affect hash, references robust against reformatting.

Error Recovery

Hash mismatch: Error shows updated LINE:HASH refs with >>> markers. Copy new refs, retry.

No-op error: Replacement matches current content. Re-read file for current state.

License

MIT