Roblox UtilitiesDevlHub Roblox Documentation

Library

debug

This library provides functions useful for debugging and profiling code.

Provides a few basic functions for debugging code in Roblox. Unlike the debug library found in Lua natively, this version has been heavily sandboxed.

Functions 11#

tracebackReturns a string of undefined format that describes the current function call stack.
tracebackReturns a string of undefined format that describes the current function call stack.
infoTraverses the entire stack of current thread and returns a string containing the call stack of target level details.
infoTraverses the entire stack of current thread and returns a string containing the call stack of target function details.
infoTraverses the entire stack of target thread and returns a string containing the call stack of target level details.
profilebeginStarts profiling for a label.
profileendStops profiling for the most recent label that debug.profilebegin() opened.
getmemorycategoryReturns the name of the current thread's active memory category.
setmemorycategoryAssigns a custom tag to the current thread's memory category.
resetmemorycategoryResets the tag assigned by debug.setmemorycategory() to the automatically assigned value (typically, the script name).
dumpcodesizeDisplays a table of native code size of individual functions and scripts.

traceback(message: string, level: number = 1): string#

Returns a traceback of the current function call stack as a string; in other words, a description of the functions that have been called up to this point. During debugging, this behaves like an error stack trace but does not stop execution of the script.

The level parameter specifies what level of the call stack to consider, with 1 being the call of debug.traceback() itself, 2 being the call of the function calling debug.traceback(), and so on. See the code sample below for an example of sequential function calls.

Note that this function will often return inaccurate results (compared to the original source code) and that the format of the returned traceback may change at any time. You should not parse the return value for specific information such as script names or line numbers.

The following example includes sequential function calls; fnB() is called, and it calls fnA() which then calls debug.traceback().

Luau
local function fnA()
	print(debug.traceback("Specific moment during fnA()"))
end

local function fnB()
	fnA()
end

-- Call function fnB() to begin traceback
fnB()
NameTypeDefaultDescription
messagestringThe first line of the returned string.
levelnumber1The number of calls "up" the call stack to return.
Returns
  • string — Traceback of the current function call stack.

traceback(thread: thread, message: string, level: number = 1): string#

Returns a traceback of the current function call stack as a string; in other words, a description of the functions that have been called up to this point. During debugging, this behaves like an error stack trace but does not stop execution of the script.

The level parameter specifies what level of the call stack to consider, with 1 being the call of debug.traceback() itself, 2 being the call of the function calling debug.traceback(), and so on. See the code sample below for an example of sequential function calls.

Note that this function will often return inaccurate results (compared to the original source code) and that the format of the returned traceback may change at any time. You should not parse the return value for specific information such as script names or line numbers.

The following example includes sequential function calls; fnB() is called, and it calls fnA() which then calls debug.traceback().

Luau
local function fnA()
	print(debug.traceback("Specific moment during fnA()"))
end

local function fnB()
	fnA()
end

-- Call function fnB() to begin traceback
fnB()
NameTypeDefaultDescription
threadthreadA thread as returned by coroutine.create().
messagestringThe first line of the returned string.
levelnumber1The number of calls "up" the call stack to return.
Returns
  • string — Traceback of the current function call stack.

info(level: number, options: string): Tuple#

Allows programmatic inspection of the call stack. This function differs from debug.traceback() in that it guarantees the format of the data it returns. This is useful for general logging and filtering purposes as well as for sending the data to systems expecting structured input, such as crash aggregation.

Luau
local function fnA()
	-- Output source identifier ("s") and line ("l") at levels 1 and 2
	print(debug.info(1, "sl"))  --> fnA() 3
	print(debug.info(2, "sl"))  --> fnA() 7
end

fnA()

Note that this function is similar to debug.getinfo, an unavailable part of the standard Lua library which serves a similar purpose.

NameTypeDefaultDescription
levelnumberDetermines at what level of the call stack the information returned should describe. A value of 1 represents the function which is calling debug.info(), a value of 2 represents the function that called that function, and so on.
optionsstring

A string that describes what the returned information should represent. It must only contain 0 or 1 instances of the characters slnaf, each representing a piece of information:

  • s (string) — The function source identifier, equal to the full name of the script the function is defined in.
  • l (number) — The line number of the function call represented by level.
  • n (string) — The name of the function; may be nil for anonymous functions and C functions without an assigned debug name.
  • a (number, boolean) — Arity of the function, which refers to the parameter count and whether the function is variadic.
  • f (function) — The function which was inspected.
Returns
  • Tuple — One value per character in options, in the order they appear: source identifier (s), line number (l), function name (n), parameter count and whether variadic (a), or the function itself (f).

info(function: function, options: string): Tuple#

Allows programmatic inspection of the call stack. This function differs from debug.traceback() in that it guarantees the format of the data it returns. This is useful for general logging and filtering purposes as well as for sending the data to systems expecting structured input, such as crash aggregation.

Luau
local function fnA()

end

local function fnB()

end

-- Output line ("l"), name ("n"), and identifier ("f") for both fnA() and fnB()
print(debug.info(fnA, "lnf"))  --> 1 fnA function: 0x75e3d3c398a81252
print(debug.info(fnB, "lnf"))  --> 5 fnB function: 0x6022a6dc5ccf4ab2

Note that this function is similar to debug.getinfo, an unavailable part of the standard Lua library which serves a similar purpose.

NameTypeDefaultDescription
functionfunctionThe function of the call stack which the information returned should describe.
optionsstring

A string that describes what the returned information should represent. It must only contain 0 or 1 instances of the characters slnaf, each representing a piece of information:

  • s (string) — The function source identifier, equal to the full name of the script the function is defined in.
  • l (number) — The line that function is defined on.
  • n (string) — The name of the function; may be nil for anonymous functions and C functions without an assigned debug name.
  • a (number, boolean) — Arity of the function, which refers to the parameter count and whether the function is variadic.
  • f (function) — The function which was inspected.
Returns
  • Tuple — One value per character in options, in the order they appear: source identifier (s), line number (l), function name (n), parameter count and whether variadic (a), or the function itself (f).

info(thread: thread, level: number, options: string): Tuple#

Allows programmatic inspection of the call stack. This function differs from debug.traceback() in that it guarantees the format of the data it returns. This is useful for general logging and filtering purposes as well as for sending the data to systems expecting structured input, such as crash aggregation.

Luau
local function fnA()
	-- Output source identifier ("s") and line ("l") at levels 1 and 2
	print(debug.info(1, "sl"))  --> fnA() 3
	print(debug.info(2, "sl"))  --> fnA() 7
end

fnA()

Note that this function is similar to debug.getinfo, an unavailable part of the standard Lua library which serves a similar purpose.

NameTypeDefaultDescription
threadthreadA thread as returned by coroutine.create().
levelnumberDetermines at what level of the call stack the information returned should describe. A value of 1 represents the function which is calling debug.info(), a value of 2 represents the function that called that function, and so on.
optionsstring

A string that describes what the returned information should represent. It must only contain 0 or 1 instances of the characters slnaf, each representing a piece of information:

  • s (string) — The function source identifier, equal to the full name of the script the function is defined in.
  • l (number) — The line number of the function call represented by level.
  • n (string) — The name of the function; may be nil for anonymous functions and C functions without an assigned debug name.
  • a (number, boolean) — Arity of the function, which refers to the parameter count and whether the function is variadic.
  • f (function) — The function which was inspected.
Returns
  • Tuple — One value per character in options, in the order they appear: source identifier (s), line number (l), function name (n), parameter count and whether variadic (a), or the function itself (f).

profilebegin(label: string): ()#

Starts profiling for a MicroProfiler label.

NameTypeDefaultDescription
labelstringThe text that this MicroProfiler label displays.
Returns
  • ()

profileend(): ()#

Stops profiling for the most recent MicroProfiler label that debug.profilebegin() opened.

Returns
  • ()

getmemorycategory(): string#

Returns the name of the current thread's active memory category.

Returns
  • string — The current thread's active memory category.

setmemorycategory(tag: string): string#

Assigns a custom tag name to the current thread's memory category in the Developer Console. Useful for analyzing memory usage of multiple threads in the same script which would otherwise be grouped together under the same tag/name. Returns the name of the current thread's previous memory category.

NameTypeDefaultDescription
tagstringThe custom name to assign to the current thread's memory category in the Developer Console.
Returns
  • string — The current thread's previous memory category.

resetmemorycategory(): ()#

Resets the tag assigned by debug.setmemorycategory() to the automatically assigned value (typically, the script name).

Returns
  • ()

dumpcodesize(): ()#

Displays a table of native code size of individual functions and scripts. This function is only available in the Command Bar in Studio. More details can be found on the Native Code Generation page.

Returns
  • ()