If you have spent any time poking around the more technical side of Luau, you have likely come across roblox debug.getconstants and wondered what it actually does for your code. It is one of those functions that feels a bit "underground" because you won't usually find it in your everyday local script inside Roblox Studio. In fact, if you try to run it in a standard environment, the engine will probably just throw an error at you. But in the world of reverse engineering, debugging, and script analysis, it is a heavy hitter that reveals exactly what is happening inside a compiled function.
To put it simply, every time you write a function in Roblox, the engine doesn't just store it as raw text. It compiles that code into something the virtual machine can understand. Part of that process involves taking all the fixed values you wrote—like strings, numbers, and booleans—and sticking them into a "constant table." The roblox debug.getconstants function is the tool used to peek inside that table and see every hardcoded value the function relies on.
What are constants anyway?
Before we get too deep into the function itself, we should probably clarify what a "constant" is in the context of the Luau VM. When you write a line like local greeting = "Hello, world!", the string "Hello, world!" is a constant. If you have a loop that runs 10 times, that number 10 is a constant.
When your script is compiled, Luau looks at these values and says, "Okay, these aren't going to change while the script is running, so I'll put them in a dedicated list for this function." This makes the code run faster because the engine doesn't have to re-evaluate the value every single time the function executes. It just looks up index #1 or index #5 in the constant table.
When you call roblox debug.getconstants on a function, it returns a table containing every single one of those values. If you have a function that prints "Winner" when a player reaches a certain score, "Winner" will be sitting right there in the constants.
Why you can't usually use it in Studio
If you are trying to use roblox debug.getconstants in a standard game you're developing, you're going to hit a wall. Roblox locks down the debug library pretty tightly for security reasons. Specifically, they use something called "capabilities" or "identity levels."
Most of the advanced debug functions are restricted to a higher identity than what a normal game script runs at. Why? Because if anyone could just grab the constants of any function, they could easily reverse-engineer core game logic, find hidden remote names, or bypass security checks by seeing exactly what strings a function is looking for.
That said, this function is a staple in custom execution environments and certain specialized debugging tools used by developers who are stress-testing their own systems. It is also a favorite for people who enjoy "de-obfuscating" scripts—taking a mess of unreadable code and trying to figure out what it's actually trying to do.
The difference between constants and upvalues
One thing that trips up a lot of people is the difference between roblox debug.getconstants and debug.getupvalues. They might sound similar because they both give you data about a function, but they are looking at two different things.
- Constants are literal values written directly into the function. If you wrote
print("Apple"), "Apple" is a constant. - Upvalues are variables defined outside the function's immediate scope that the function still uses. If you have a variable
local x = 5and a function inside that script usesx, thenxis an upvalue.
If you use roblox debug.getconstants, you'll see the "Apple," but you won't see x. Understanding this distinction is huge when you are trying to map out how a script works. Constants tell you the "what," while upvalues often tell you the "where" (in terms of state and external data).
Breaking down a practical example
Let's imagine you have a simple function. It isn't doing anything fancy, just checking a value:
lua function checkSecret(input) if input == "OpenSesame123" then print("Access Granted") else print("Access Denied") end end
In a hypothetical environment where roblox debug.getconstants is allowed, calling it on checkSecret would return a table that looks something like this: { "OpenSesame123", "Access Granted", "Access Denied" }.
Notice how the logic—the if statement and the comparison—isn't there. You only get the "ingredients" of the function. However, even just having the ingredients is incredibly powerful. If you didn't know the password to that function, a quick peek at the constants would give it away instantly. This is exactly why game developers need to be careful about hardcoding sensitive information directly into their client-side scripts.
Using getconstants for script optimization
While a lot of the talk around roblox debug.getconstants involves security, it is also a pretty cool tool for learning how Luau optimizes your code. Sometimes, you might think you're being clever with how you've written a bit of logic, but the compiler sees it differently.
By looking at the constants, you can see if the compiler has "folded" certain values. For example, if you write local seconds = 60 * 60, the compiler is smart enough to just put 3600 into the constant table instead of making the computer do the math every time the script runs. Seeing this in action helps you understand what the Luau VM is doing under the hood, which ultimately makes you a better scripter.
The role in reverse engineering
In the broader Roblox community, you will often see roblox debug.getconstants mentioned in forums or Discord servers dedicated to "exploiting" or "scripting utilities." In those contexts, it is used to "hook" functions.
If a player wants to change how a gun works in a game, they might use a tool to find the function responsible for recoil. By using roblox debug.getconstants, they can find the specific number used for the recoil strength. Once they have that, they can use other functions (like debug.setconstant) to overwrite that number with a 0.
It is a cat-and-mouse game. Developers try to hide their constants or use math to generate them dynamically so they don't appear in the table as plain numbers, and others use tools to find them anyway. It's a fascinating look at how code is actually stored and modified in real-time.
Limitations and quirks
It is worth noting that roblox debug.getconstants isn't a magic wand. There are plenty of things it won't show you. For instance, it doesn't show you local variable names. If you have local mySuperSecretVariable = 50, the table will just show 50. The name mySuperSecretVariable is completely stripped out during compilation because the computer doesn't need it to run the code.
Also, Luau is constantly being updated. The way the VM handles constants can change. Sometimes values are reused across different functions to save memory (constant pooling), which can make the output of these debug functions a bit more complex than you'd expect.
Wrapping it up
At the end of the day, roblox debug.getconstants is a window into the inner workings of Luau. Even if you aren't using it in your daily workflow to build a simulator or an obby, knowing it exists gives you a much better grasp of how Roblox handles your code once you hit that "Publish" button.
It reminds us that our scripts aren't just blocks of text—they are structured data. Every string, every number, and every hardcoded boolean is tucked away in a table, waiting for the VM to grab it. Whether you're interested in it for security, optimization, or just pure curiosity, it's one of the most interesting "hidden" parts of the Roblox scripting ecosystem. Just don't expect it to work in your standard LocalScript without some very specific (and usually third-party) circumstances!