Edit File Lines MCP Server

A TypeScript-based MCP server that provides tools for making precise line-based edits to text files within allowed directories.

Features

Main Editing Tool

edit_file_lines

Make line-based edits to a file using string or regex pattern matching. Each edit can:

• Replace entire lines
• Replace specific text matches while preserving line formatting
• Use regex patterns for complex matches
• Handle multiple lines and multiple edits
• Preview changes with dry run mode

Example file (src/components/App.tsx):

// Basic component with props
const Button = ({ color = "blue", size = "md" }) => {
  return <button className={`btn-${color} size-${size}`}>Click me</button>;
};

// Component with multiple props and nested structure
export const Card = ({
  title,
  subtitle = "Default subtitle",
  theme = "light",
  size = "lg",
}) => {
  const cardClass = `card-${theme} size-${size}`;
  
  return (
    <div className={cardClass}>
      <h2>{title}</h2>
      <p>{subtitle}</p>
    </div>
  );
};

// Constants and configurations
const THEME = {
  light: { bg: "#ffffff", text: "#000000" },
  dark: { bg: "#000000", text: "#ffffff" },
};

const CONFIG = {
  apiUrl: "https://api.example.com",
  timeout: 5000,
  retries: 3,
};

Example Use Cases

1. Simple String Replacement

{
  "p": "src/components/App.tsx",
  "e": [{
    "startLine": 2,
    "endLine": 2,
    "content": "primary",
    "strMatch": "blue"
  }],
  "dryRun": true
}

Output:

Index: src/components/App.tsx
===================================================================
--- src/components/App.tsx        original
+++ src/components/App.tsx        modified
@@ -1,6 +1,6 @@
 // Basic component with props
-const Button = ({ color = "blue", size = "md" }) => {
+const Button = ({ color = "primary", size = "md" }) => {
   return Click me;
 };
 
 // Component with multiple props and nested structure

State ID: fcbf740a Use this ID with approve_edit to apply the changes.

2. Multi-line Content with Preserved Structure

{
  "p": "src/components/App.tsx",
  "e": [{
    "startLine": 16,
    "endLine": 19,
    "content": "    <div className={cardClass}>\n      <h2 className=\"title\">{title}</h2>\n      <p className=\"subtitle\">{subtitle}</p>\n    </div>",
    "regexMatch": "<div[^>]*>[\\s\\S]*?</div>"
  }],
  "dryRun": true
}

Output:

Index: src/components/App.tsx
===================================================================
--- src/components/App.tsx        original
+++ src/components/App.tsx        modified
@@ -13,10 +13,10 @@
   const cardClass = `card-${theme} size-${size}`;
   
   return (
     <div className={cardClass}>
-      <h2>{title}</h2>
-      <p>{subtitle}</p>
+      <h2 className="title">{title}</h2>
+      <p className="subtitle">{subtitle}</p>
     </div>
   );
 };

State ID: f2ce973f Use this ID with approve_edit to apply the changes.

3. Complex JSX Structure Modification

{
  "p": "src/components/App.tsx",
  "e": [{
    "startLine": 7,
    "endLine": 12,
    "content": "export const Card = ({\n  title,\n  subtitle = \"New default\",\n  theme = \"modern\",\n  size = \"responsive\"\n}) => {",
    "regexMatch": "export const Card[\\s\\S]*?\\) => \\{"
  }],
  "dryRun": true
}

Output:

Index: src/components/App.tsx
===================================================================
--- src/components/App.tsx        original
+++ src/components/App.tsx        modified
@@ -5,11 +5,11 @@
 // Component with multiple props and nested structure
 export const Card = ({
   title,
-  subtitle = "Default subtitle",
-  theme = "light",
-  size = "lg",
+  subtitle = "New default",
+  theme = "modern",
+  size = "responsive"
 }) => {
   const cardClass = `card-${theme} size-${size}`;
   
   return (

State ID: f1f1d27b Use this ID with approve_edit to apply the changes.

4. Configuration Update with Whitespace Preservation

{
  "p": "src/components/App.tsx",
  "e": [{
    "startLine": 29,
    "endLine": 32,
    "content": "const CONFIG = {\n  baseUrl: \"https://api.newexample.com\",\n  timeout: 10000,\n  maxRetries: 5",
    "regexMatch": "const CONFIG[\\s\\S]*?retries: \\d+"
  }],
  "dryRun": true
}

Output:

Index: src/components/App.tsx
===================================================================
--- src/components/App.tsx        original
+++ src/components/App.tsx        modified
@@ -26,8 +26,8 @@
   dark: { bg: "#000000", text: "#ffffff" },
 };
 
 const CONFIG = {
-  apiUrl: "https://api.example.com",
-  timeout: 5000,
-  retries: 3,
+  baseUrl: "https://api.newexample.com",
+  timeout: 10000,
+  maxRetries: 5
 };

State ID: 20e93c34 Use this ID with approve_edit to apply the changes.

5. Flexible Whitespace Matching

{
  "p": "src/components/App.tsx",
  "e": [{
    "startLine": 9,
    "endLine": 9,
    "content": "description",
    "strMatch": "subtitle   =   \"Default subtitle\""  // Extra spaces are handled
  }],
  "dryRun": true
}

Output:

Index: src/components/App.tsx
===================================================================
--- src/components/App.tsx        original
+++ src/components/App.tsx        modified
@@ -5,9 +5,9 @@
 // Component with multiple props and nested structure
 export const Card = ({
   title,
-  subtitle = "Default subtitle",
+  description
   theme = "light",
   size = "lg",
 }) => {
   const cardClass = `card-${theme} size-${size}`;

Additional Tools

approve_edit

Apply changes from a previous dry run of edit_file_lines. This tool provides a two-step editing process for safety. Here is an example workflow:

1. First, make a dry run edit:

{
  "p": "src/components/App.tsx",
  "e": [{
    "startLine": 2,
    "endLine": 2,
    "content": "primary",
    "strMatch": "blue"
  }],
  "dryRun": true
}

Output:

Index: src/components/App.tsx
===================================================================
--- src/components/App.tsx        original
+++ src/components/App.tsx        modified
@@ -1,6 +1,6 @@
 // Basic component with props
-const Button = ({ color = "blue", size = "md" }) => {
+const Button = ({ color = "primary", size = "md" }) => {
   return <button className={`btn-${color} size-${size}`}>Click me</button>;
 };

State ID: fcbf740a Use this ID with approve_edit to apply the changes.

2. Then, approve the changes using the state ID:

{
  "stateId": "fcbf740a"
}

Output:

Index: src/components/App.tsx
===================================================================
--- src/components/App.tsx        original
+++ src/components/App.tsx        modified
@@ -1,6 +1,6 @@
 // Basic component with props
-const Button = ({ color = "blue", size = "md" }) => {
+const Button = ({ color = "primary", size = "md" }) => {
   return <button className={`btn-${color} size-${size}`}>Click me</button>;
 };

3. Verify the changes:

{
  "path": "src/components/App.tsx",
  "lineNumbers": [2],
  "context": 1
}

Output:

Line 2:
  1: // Basic component with props
> 2: const Button = ({ color = "primary", size = "md" }) => {
  3:   return <button className={`btn-${color} size-${size}`}>Click me</button>;

Note that state IDs expire after a short time for security. Attempting to use an expired or invalid state ID will result in an error:

{
  "stateId": "invalid123"
}

Output:

Error: Invalid or expired state ID

get_file_lines

Inspect specific lines in a file with optional context lines. This tool is useful for verifying line content before making edits.

{
  "path": "src/components/App.tsx",
  "lineNumbers": [1, 2, 3],
  "context": 1
}

Output:

Line 1:
> 1: // Basic component with props
  2: const Button = ({ color = "blue", size = "md" }) => {

Line 2:
  1: // Basic component with props
> 2: const Button = ({ color = "blue", size = "md" }) => {
  3:   return Click me;

Line 3:
  2: const Button = ({ color = "blue", size = "md" }) => {
> 3:   return Click me;
  4: };

search_file

Search a file for text patterns or regular expressions to find specific line numbers and their surrounding context. This tool is particularly useful for locating the exact lines you want to edit with edit_file_lines.

Features:

• Simple text search with optional case sensitivity
• Regular expression support
• Whole word matching
• Configurable context lines
• Returns line numbers, content, and surrounding context with line numbers

Arguments:

{
  path: string;          // Path to the file to search
  pattern: string;       // Search pattern (text or regex)
  type?: "text" | "regex"; // Type of search (default: "text")
  caseSensitive?: boolean; // Case-sensitive search (default: false)
  contextLines?: number;   // Number of context lines (default: 2, max: 10)
  maxMatches?: number;     // Maximum matches to return (default: 100)
  wholeWord?: boolean;     // Match whole words only (default: false)
  multiline?: boolean;     // Enable multiline regex mode (default: false)
}

Example use cases:

1. Simple text search:

{
  "path": "src/components/App.tsx",
  "pattern": "const",
  "contextLines": 2
}

Output:

Found 6 matches in 0.9ms:
File size: 0.7KB

Match 1: Line 2, Column 1
----------------------------------------
     1 | // Basic component with props
>    2 | const Button = ({ color = "blue", size = "md" }) => {
     3 |   return <button className={`btn-${color} size-${size}`}>Click me</button>;
     4 | };

Match 2: Line 7, Column 8
----------------------------------------
     5 | 
     6 | // Component with multiple props and nested structure
>    7 | export const Card = ({
     8 |   title,
     9 |   subtitle = "Default subtitle",

Match 3: Line 13, Column 3
----------------------------------------
    11 |   size = "lg",
    12 | }) => {
>   13 |   const cardClass = `card-${theme} size-${size}`;
    14 |   
    15 |   return (

Match 4: Line 23, Column 4
----------------------------------------
    21 | };
    22 | 
>   23 | // Constants and configurations
    24 | const THEME = {
    25 |   light: { bg: "#ffffff", text: "#000000" },

Match 5: Line 24, Column 1
----------------------------------------
    22 | 
    23 | // Constants and configurations
>   24 | const THEME = {
    25 |   light: { bg: "#ffffff", text: "#000000" },
    26 |   dark: { bg: "#000000", text: "#ffffff" },

Match 6: Line 29, Column 1
----------------------------------------
    27 | };
    28 | 
>   29 | const CONFIG = {
    30 |   apiUrl: "https://api.example.com",
    31 |   timeout: 5000,

2. Case-sensitive whole word search:

{
  "path": "src/components/App.tsx",
  "pattern": "props",
  "caseSensitive": true,
  "wholeWord": true,
  "contextLines": 1
}

Output:

Found 2 matches in 0.7ms:
File size: 0.7KB

Match 1: Line 1, Column 25
----------------------------------------
>    1 | // Basic component with props
     2 | const Button = ({ color = "blue", size = "md" }) => {

Match 2: Line 6, Column 28
----------------------------------------
     5 | 
>    6 | // Component with multiple props and nested structure
     7 | export const Card = ({

3. Finding JSX components:

{
  "path": "src/components/App.tsx",
  "pattern": "<[A-Z]\\w+\\s",
  "type": "regex",
  "contextLines": 1
}

Output:

Found 2 matches in 0.6ms:
File size: 0.7KB

Match 1: Line 3, Column 10
----------------------------------------
     2 | const Button = ({ color = "blue", size = "md" }) => {
>    3 |   return <button className={`btn-${color} size-${size}`}>Click me</button>;
     4 | };

Match 2: Line 16, Column 5
----------------------------------------
    15 |   return (
>   16 |     <div className={cardClass}>
    17 |       <h2>{title}</h2>

Common workflows:

1. Find then edit:

// First, search for the line
{
  "path": "src/config.ts",
  "pattern": "API_URL",
  "wholeWord": true
}

// Then use the returned line number in edit_file_lines
{
  "p": "src/config.ts",
  "e": [{
    "startLine": 23,  // Line number from search result
    "endLine": 23,
    "content": "export const API_URL = 'https://new-api.example.com';"
  }]
}

2. Find all usages:

{
  "path": "src/components/App.tsx",
  "pattern": "\\buseMemo\\b",
  "type": "regex",
  "contextLines": 2,
  "maxMatches": 50
}

3. Find specific prop patterns:

{
  "path": "src/components/App.tsx",
  "pattern": "className=['\"]([^'\"]+)['\"]",
  "type": "regex",
  "contextLines": 1
}

Important Notes

1. Whitespace Handling

   • The tool intelligently handles whitespace in both string and regex matches
   • Original indentation is preserved in replacements
   • Multiple spaces between tokens are normalized for matching

2. Pattern Matching

   • String matches (strMatch) are whitespace-normalized
   • Regex patterns (regexMatch) support look-ahead and look-behind
   • Cannot use both strMatch and regexMatch in the same edit
   • Overlapping regex patterns are detected and prevented

3. Best Practices

   • Always use dry run first to verify changes
   • Review the diff output before approving changes
   • Keep edit operations focused and atomic
   • Use appropriate pattern matching for your use case

Development

Install dependencies:

npm install

Build the server:

npm run build

For development with auto-rebuild:

npm run watch

Testing

Run the test suite:

npm run test

Additional testing utilities:

Test Tools Script

Test the MCP tools directly against sample files:

npm run test:tools

This script:

• Resets test fixtures to a known state
• Connects to the MCP server
• Tests each tool in sequence:
  • get_file_lines
  • edit_file_lines (dry run)
  • approve_edit
• Shows the output of each operation
• Verifies changes were applied correctly

Reset Fixtures Script

Reset test fixtures to their original state:

npm run reset:fixtures

Use this script to:

• Reset test files to a known state before testing
• Clean up after failed tests
• Ensure consistent test environment
• Create missing fixture directories

Usage

The server requires one or more allowed directories to be specified when starting:

node build/index.js <allowed-directory> [additional-directories...]

All file operations will be restricted to these directories for security.

Environment Variables

• MCP_EDIT_STATE_TTL: Time-to-live in milliseconds for edit states (default: 60000). Edit states will expire after this duration and must be recreated.

Installation

To use with Claude Desktop, add the server config:

On MacOS: ~/Library/Application Support/Claude/claude_desktop_config.json On Windows: %APPDATA%/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "edit-file-lines": {
      "command": "node",
      "args": [
        "/path/to/edit-file-lines/build/index.js",
        "<allowed-directory>"
      ],
      "env": {
        "MCP_EDIT_STATE_TTL": "300000"  // Optional: Set custom TTL (in milliseconds)
      }
    }
  }
}

Error Handling

The tool provides clear error messages for common issues:

1. Match Not Found

Error: No string match found for "oldValue" on line 5

2. Invalid Regex

Error: Invalid regex pattern "([": Unterminated group

3. Multiple Edits on Same Line

Error: Line 5 is affected by multiple edits

Security Considerations

• All file operations are restricted to explicitly allowed directories
• Symlinks are validated to prevent escaping allowed directories
• Parent directory traversal is prevented
• Path normalization is performed for consistent security checks
• Invalid line numbers and character positions are rejected
• Line ending normalization ensures consistent behavior across platforms
• Edit states expire after 60 seconds for security
• Edit approvals require exact match of file path and edits

Debugging

Use the Test Tools script to test the MCP tools directly against sample files. The MCP Inspector might help, but it currently does not support handing input that are not string values.