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Overview

Replace specific lines in a Roblox script without rewriting the entire source. Provides precise, line-level editing for efficient script modifications.
Line numbers are 1-indexed and ranges are inclusive. Always use the numberedSource field from get_script_source to identify correct line numbers.

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Parameters

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instancePath
string
required
Roblox instance path to the script using dot notationExamples:
  • game.ServerScriptService.MainScript
  • game.StarterPlayer.StarterPlayerScripts.LocalScript
  • game.ReplicatedStorage.Modules.DataManager
​
startLine
number
required
First line to replace (1-indexed)Get from numberedSource field of get_script_source
​
endLine
number
required
Last line to replace (inclusive)Get from numberedSource field of get_script_source
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newContent
string
required
New content to replace the specified lines
  • Can be single line or multiple lines (separated by \n)
  • Preserves indentation exactly as provided
  • Must be valid Lua syntax

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Response

{
  "success": true,
  "message": "Lines 45-47 replaced successfully",
  "linesReplaced": 3,
  "newLineCount": 2,
  "totalLines": 156
}
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success
boolean
Whether the operation completed successfully
​
message
string
Status message describing the operation
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linesReplaced
number
Number of lines removed (endLine - startLine + 1)
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newLineCount
number
Number of lines added
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totalLines
number
Total lines in script after edit

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Usage Examples

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Replace Single Line

{
  "instancePath": "game.ServerScriptService.MainScript",
  "startLine": 12,
  "endLine": 12,
  "newContent": "    print('Updated message')"
}

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Replace Function Body

Before (lines 45-47): 
45: local function onPlayerJoin(player)
46:     print('Player joined:', player.Name)
47: end
Request: 
{
  "instancePath": "game.ServerScriptService.PlayerHandler",
  "startLine": 46,
  "endLine": 46,
  "newContent": "    print('Welcome!', player.Name)\n    player:SetAttribute('JoinTime', os.time())"
}
After (lines 45-48): 
45: local function onPlayerJoin(player)
46:     print('Welcome!', player.Name)
47:     player:SetAttribute('JoinTime', os.time())
48: end

​
Replace Multiple Lines

Before (lines 20-25): 
20: local function calculateDamage(attacker, target)
21:     local damage = 10
22:     target.Health = target.Health - damage
23:     print('Damage dealt:', damage)
24:     return damage
25: end
Request: 
{
  "instancePath": "game.ServerScriptService.Combat",
  "startLine": 21,
  "endLine": 23,
  "newContent": "    local baseDamage = 10\n    local multiplier = attacker:GetAttribute('Strength') or 1\n    local damage = baseDamage * multiplier\n    target.Health = math.max(0, target.Health - damage)\n    print('Damage dealt:', damage, 'to', target.Name)"
}
After (lines 20-27): 
20: local function calculateDamage(attacker, target)
21:     local baseDamage = 10
22:     local multiplier = attacker:GetAttribute('Strength') or 1
23:     local damage = baseDamage * multiplier
24:     target.Health = math.max(0, target.Health - damage)
25:     print('Damage dealt:', damage, 'to', target.Name)
26:     return damage
27: end

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Best Practices

Step 1: Call get_script_source to get current line numbers
{"instancePath": "game.ServerScriptService.Script"}
Step 2: Find target lines in numberedSource:
15: local function example()
16:     print('old code')
17: end
Step 3: Use exact line numbers from numberedSource:
{
  "instancePath": "game.ServerScriptService.Script",
  "startLine": 16,
  "endLine": 16,
  "newContent": "    print('new code')"
}
Match the indentation of surrounding code:
-- Function at root level (no indent)
function example()
    -- Content indented 4 spaces
    if condition then
        -- Nested content indented 8 spaces
        print('Hello')
    end
end
When editing line 19 (inside if statement), use 12 spaces:
{
  "startLine": 19,
  "endLine": 19,
  "newContent": "            print('Properly indented')"
}
Use \n to separate lines in newContent:
{
  "startLine": 10,
  "endLine": 10,
  "newContent": "    local a = 1\n    local b = 2\n    return a + b"
}
This replaces line 10 with 3 new lines.
startLine to endLine includes both endpoints:
  • startLine: 5, endLine: 5 → replaces line 5 only
  • startLine: 5, endLine: 7 → replaces lines 5, 6, and 7
  • startLine: 5, endLine: 10 → replaces 6 lines total
After making edits, verify the script still has valid syntax:
-- Use execute_lua tool:
local script = game.ServerScriptService.MainScript
local source = script.Source
local fn, err = loadstring(source)
return err or "Syntax OK"

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Common Patterns

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Update Function Logic

Replace function body
{
  "instancePath": "game.ServerScriptService.Utils",
  "startLine": 15,
  "endLine": 17,
  "newContent": "    -- Updated implementation\n    return value * 2"
}

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Fix Bug in Specific Lines

Fix off-by-one error
{
  "instancePath": "game.ServerScriptService.GameManager",
  "startLine": 42,
  "endLine": 42,
  "newContent": "    for i = 1, #players do  -- Fixed: was 0, #players"
}

​
Update Variable Declaration

Change variable initialization
{
  "instancePath": "game.ServerScriptService.Config",
  "startLine": 3,
  "endLine": 3,
  "newContent": "local MAX_PLAYERS = 20  -- Updated from 10"
}

get_script_source

Read script with line numbers

set_script_source

Replace entire script

insert_script_lines

Insert new lines

delete_script_lines

Delete line ranges

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Error Handling

{
  "error": "Invalid line range: startLine must be <= endLine",
  "startLine": 50,
  "endLine": 40
}

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Complete Workflow Example

Step 1: Read current source
{
  "name": "get_script_source",
  "arguments": {
    "instancePath": "game.ServerScriptService.GameManager"
  }
}
Step 2: Analyze numberedSource
42: local function startRound()
43:     print('Round starting')
44:     roundActive = true
45: end
Step 3: Edit specific
{
  "name": "edit_script_lines",
  "arguments": {
    "instancePath": "game.ServerScriptService.GameManager",
    "startLine": 43,
    "endLine": 44,
    "newContent": "    print('Round starting in 3 seconds...')\n    task.wait(3)\n    roundActive = true\n    print('Round active!')"
  }
}
Step 4: Result
42: local function startRound()
43:     print('Round starting in 3 seconds...')
44:     task.wait(3)
45:     roundActive = true
46:     print('Round active!')
47: end

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