OnlineGDB: How to Use the Free Online GDB Debugger

OnlineGDB (onlinegdb.com) is a free, browser-based compiler and debugger built on gcc/g++ and GDB. You paste or write C or C++ code, click Debug, set breakpoints by clicking next to line numbers, press start, and step through the program while watching local variables and the call stack, with nothing to install. It also compiles and runs dozens of other languages, and as of November 2026 its debugger also works for Python 3 (through pdb) and Java, which many older guides get wrong.

If you landed here after typing "online gdb", "gdb online", "online.gdb" or a quick typo like online gbd, online gdp, onlinegbd or "gbd online debugger", they all point to the same site. This guide covers everything the site itself leaves out: exact limits, compiler versions, every debugger button, a GDB command cheat sheet, how to debug Python and Java, what the common error messages mean, and the best alternatives when OnlineGDB is not enough.

What OnlineGDB is

OnlineGDB, the online GDB compiler and debugger at onlinegdb.com, describes itself as an "online compiler and debugger for C/C++". Under the hood it compiles with gcc/g++ and debugs with GDB, the GNU debugger, and gives you a web UI on top: an editor, a console for program input and output, and debugger panels. Its About page calls it the first online IDE with an embedded gdb debugger, and the site footer dates it to 2016.

GDB is the name of the debugger, not the compiler. People sometimes call the site a "gdb compiler", but the compiling is done by gcc (for C) and g++ (for C++); GDB is the tool that pauses the compiled program, lets you inspect it and steps through it. OnlineGDB is a single website that bundles both, which is why "gdb online debugger" and "online gdb compiler" end up on the same page.

You can use it without an account. Signing in (Google, Facebook or GitHub) gives you an online GDB account, which lets you save projects under My Projects and create share links that never expire. The free site shows ads; a Remove Ads button links to a premium upgrade page.

Languages it supports

The language menu on onlinegdb.com lists 47 entries as of November 2026: C, C++ (plus C++14, C++17, C++20, C++23 and C++26), C and C++ in TurboC mode, Java, Python 3, Kotlin, PHP, C# (Mono and .NET), OCaml, VB, HTML/JS/CSS, Ruby, Perl, Pascal, PascalABC.NET, COBOL, R, Fortran, Haskell, Assembly (GCC and NASM), Objective-C, SQLite, Dart, Smalltalk, Groovy, Tcl, C3, Lua, Zig, TypeScript, D, Ada, JavaScript (Rhino and Node), Prolog, Swift, Rust, Go and Bash.

Every one of those can be compiled and run. Debugging is narrower:

Language	Run	Step debugger	What powers it
C, C++ (all standards)	Yes	Yes	gcc/g++ + GDB
Assembly (GCC, NASM)	Yes	Registers panel is there for low-level work	GDB
Python 3	Yes	Yes (tested November 2026)	Python 3.8.10 + pdb
Java	Yes	Yes (tested November 2026)	JVM debugger, via the Java debugger page
Everything else	Yes	Run-only in practice	Language's own compiler or interpreter

Compiler and debugger versions

The OnlineGDB FAQ publishes the exact toolchain. As of November 2026:

Language mode	Compiler	Standard flag	Debugger
C	gcc 11.4.0	-std=gnu99	gdb 12.1
C++	g++ 11.4.0	-std=c++11	gdb 12.1
C++14	g++ 11.4.0	-std=c++14	gdb 12.1
C++17	g++ 13.1.0	-std=c++17	gdb 12.1
C++20	g++ 13.1.0	-std=c++20	gdb 12.1
C++23	g++ 13.1.0	-std=c++2b	gdb 12.1
C++26	g++ 16.1.0	-std=c++26	gdb 17.1
Python 3	python3 3.8.10	n/a	pdb 3.8.10
Rust	rustc 1.61.0	n/a	none listed
Fortran	gfortran 11.3.0	n/a	none listed

Two practical consequences. First, plain C mode is gnu99, so if you want C11 or C17 features, add -std=c11 or -std=c17 in Extra Compiler Flags. Second, if your C++ code uses newer library features (for example std::print or std::expected), pick C++23 or C++26 in the menu, because plain "C++" means C++11 on an older compiler. The only third-party libraries the FAQ lists for C/C++ are ncurses and LAPACK.

How those versions line up with upstream releases:

1. 2016OnlineGDB launches (the site footer reads 2016 to 2026).
2. May 1, 2022GDB 12.1 released. Still OnlineGDB's debugger for C and most C++ modes.
3. Apr 26, 2023GCC 13.1 released; OnlineGDB uses 13.1.0 for C++17, C++20 and C++23.
4. May 29, 2023GCC 11.4 released; OnlineGDB uses 11.4.0 for C, C++11 and C++14.
5. Dec 20, 2025GDB 17.1 released; OnlineGDB pairs it with the C++26 mode.
6. Apr 30, 2026GCC 16.1 released; OnlineGDB uses g++ 16.1.0 for C++26.
7. Sep 25, 2026GDB 18.1 released, the latest upstream version as of November 2026.

Editor features and keyboard shortcuts

The settings (gear) menu lets you switch the editor theme (dark or light), the editor mode (Normal, Emacs or vim key bindings), font size, tab width (1 to 8 spaces), autocomplete and word wrap. The toolbar has Run (with a dropdown that includes Run with display screen (beta) and Download all files), Debug, Stop, Share, Save and { } Beautify, which reformats messy code.

The shortcuts worth memorizing, from OnlineGDB's own shortcut list:

Action	Shortcut
Run code	F9
Debug code	F8
Save project	Ctrl+S
Beautify code	Ctrl+B
New file	Ctrl+M
Go to line	Ctrl+L
Toggle comment	Ctrl+/
Find / replace	Ctrl+F / Ctrl+H
Go to next error	Alt+E

How to debug C or C++ in OnlineGDB, step by step

1. Open onlinegdb.com and pick C or C++ (or a specific standard such as C++20) from the Language menu in the top-right corner.
2. Write or paste your code. Here is a small program with a bug you can try:

#include <stdio.h>

int sum_to(int n) {
    int total = 0;
    for (int i = 1; i < n; i++) {   /* bug: should be i <= n */
        total += i;
    }
    return total;
}

int main(void) {
    int n = 5;
    printf("sum_to(%d) = %d\n", n, sum_to(n));  /* expect 15, prints 10 */
    return 0;
}

3. Set a breakpoint. Click the blank gutter to the left of a line number, for example the total += i; line. A red dot marks the breakpoint. Per OnlineGDB's own debugger guide, execution will pause each time it reaches that line. You can also set breakpoints by typing commands in the GDB console.
4. Click Debug in the toolbar (next to Run), or press F8. The program compiles with debug info and a debug session opens. The bottom pane switches to Debug Console, and a toolbar appears with start, pause, continue, step over, step into, step out and help.
5. Click start. The program runs under GDB and stops at your first breakpoint. The current line is highlighted in the editor.
6. Step through the code with the debugger buttons:
   • continue: run until the next breakpoint.
   • step over: run the current line without going inside function calls.
   • step into: go inside the function called on the current line.
   • step out: finish the current function and stop in its caller.
   • pause: interrupt a running program, for example one stuck in a loop.
7. Watch your variables. While paused, the Local Variables panel shows each local and its value (here total, i and n). The Call Stack panel shows which function called which, with file and line. In the example, you will see the loop exit when i is 5 without adding it, which is the bug.
8. Use the extra panels when you need them. Display Expressions lets you add an expression (such as total + i or arr[2]) that is re-evaluated at every stop. Breakpoints and Watchpoints lists everything you have set, with an x to remove each one. Registers shows CPU registers, which is useful for the Assembly modes.
9. Type GDB commands directly if you prefer. The Debug Console accepts standard GDB commands while debugging, for example:

break sum_to
run
next
step
print total
watch total
info locals
backtrace
continue

A watch total watchpoint stops the program every time total changes, which is often faster than stepping through a long loop. The GDB manual documents every command, and the cheat sheet below covers the ones you will actually use.

10. Fix the bug (i <= n), click Run, and confirm the output is sum_to(5) = 15.

For a longer walk-through of stepping, with a C++ example and more on the call stack, see DevHunt's OnlineGDB breakpoints and stepping tutorial.

Debugger buttons and their GDB equivalents

Each button sends a GDB command for you. Knowing the mapping helps when you move to a terminal or another IDE:

OnlineGDB button	What it does	GDB command
start	Starts the program under the debugger	run
pause	Interrupts the running program	Ctrl+C in a terminal
continue	Runs to the next breakpoint	continue (c)
step over	Runs the current line, treating function calls as one step	next (n)
step into	Enters the function called on the current line	step (s)
step out	Runs until the current function returns	finish
Breakpoint (gutter click)	Pauses when a line is reached	break <line> (b)
Local Variables panel	Shows locals of the selected frame	info locals
Call Stack panel	Shows the chain of calls	backtrace (bt)
Display Expressions panel	Re-evaluates expressions at each stop	display <expr>

Debugging a crash (segmentation fault) with the call stack

Off-by-one bugs are the classic first example, but the debugger earns its keep on crashes. When a C program dies with "Segmentation fault" in Run mode, you get no clue where. In Debug mode, GDB stops at the exact instruction:

#include <stdio.h>
#include <string.h>

void copy_name(char *dst, const char *src) {
    strcpy(dst, src);
}

int main(void) {
    char *name = NULL;          /* bug: never allocated */
    copy_name(name, "DevHunt");
    printf("%s\n", name);
    return 0;
}

1. Click Debug, then start, with no breakpoints at all.
2. GDB reports Program received signal SIGSEGV, Segmentation fault. and stops.
3. Read the Call Stack panel (or type bt). The top frame is inside the C library's string copy routine (its exact name varies), followed by copy_name and then main, each with a line number.
4. Type frame 1 to select copy_name, then print dst. GDB shows 0x0: a null pointer. That is the bug.
5. Fix it with real storage, for example char name[32];, and rerun.

The same pattern works for array overruns, use-after-free and stack overflows from runaway recursion: let it crash under the debugger, read the stack from the top, then select the first frame that is your code.

Debugging an infinite loop

If your program never finishes, clicking Run just ends in a runtime-exceeded error. Instead, click Debug, then start, wait a second, and press pause. The editor highlights the line the program was executing, and Local Variables shows the loop counter. Typing info locals a few times between continue and pause usually makes it obvious which variable never reaches its exit condition.

Debugging Python and Java on OnlineGDB

Older guides (including an earlier version of this page) say Python debugging is not supported. That is out of date. On November 4, 2026, we opened the Online Python Debugger page, clicked Debug, and got a live pdb session: the Debug Console showed the (Pdb) prompt paused on line 1, with Call Stack and Local Variables filled in. The FAQ lists the debugger as pdb 3.8.10. The site still contains a leftover "Debug mode for python program is not yet supported" message in its page code, which is probably why the myth persists.

How Python debugging differs from C/C++ on OnlineGDB:

• The session pauses on the first line right away, so you don't need start. Use continue to run to your first breakpoint.
• The console speaks pdb, not GDB. Use b 5, n, s, r, c, p total and w (see the cheat sheet below and the pdb documentation).
• It is Python 3.8.10, released years ago. Syntax from newer versions, such as match statements (3.10) or except* (3.11), will fail with a SyntaxError before you even reach the debugger.

Try it with this small bug:

def average(nums):
    total = 0
    for n in nums:
        total += n
    return total / len(nums)

print(average([4, 8, 15]))
print(average([]))   # ZeroDivisionError

Click Debug. When the (Pdb) prompt appears, type b 5 (a breakpoint on the return line), then c to continue, then p nums, total. The first stop shows ([4, 8, 15], 27); press continue again and the second shows ([], 0), which is the case you forgot to handle.

Java works the same way from the Online Java Debugger page (or by choosing Java in the language menu): click Debug, then start, and breakpoints you set in Main.java appear in the Breakpoints and Watchpoints panel while Call Stack shows JVM frames. If you searched for an "online jdb" (the JDK's command-line Java debugger), this is the closest browser equivalent.

GDB command cheat sheet

Everything below works in OnlineGDB's Debug Console for C and C++, and in any terminal gdb. The last column gives the pdb command for Python sessions. Sources: the GDB manual and the pdb docs.

Task	GDB command	Short form	pdb (Python)
Start the program	run [args]	r	starts paused automatically
Breakpoint at a line	break 12	b 12	b 12
Breakpoint at a function	break sum_to	b sum_to	b average
Conditional breakpoint	break 12 if i == 4	b 12 if i == 4	b 12, i == 4
One-time breakpoint	tbreak 12	tb 12	tbreak 12
List breakpoints	info breakpoints	i b	b
Delete breakpoint 1	delete 1	d 1	cl 1
Continue	continue	c	c
Step over	next	n	n
Step into	step	s	s
Step out	finish	fin	r
Run until line 20	until 20	u 20	unt 20
Print a value	print total	p total	p total
Print in hex	print/x n	p/x n	p hex(n)
Print 5 elements behind a pointer	print *arr@5	p *arr@5	p arr[:5]
Show a value at every stop	display total	disp total	display total
Stop when a variable changes	watch total		no equivalent
Local variables	info locals	i lo	pp locals()
Function arguments	info args		a
Call stack	backtrace	bt	w
Select a frame	frame 1, up, down	f 1	u, d
Show source around here	list	l	l or ll
Change a variable	set var n = 10		!n = 10
Show a type	ptype node		p type(node)
Examine memory (4 ints)	x/4dw arr		n/a
Quit	quit	q	q

Input, files and sharing

• Standard input. By default the console is interactive: when your program calls scanf or std::cin, type the value in the console. In debug mode the console also pauses at input points so you can type. You can switch Standard Input to Text and paste all input up front, which is handy for competitive-programming test cases. In Text mode the run is capped at 10 seconds; in interactive mode it can run until it finishes or you go idle for 15 minutes. If a program waits for input you never give, it ends with a runtime-exceeded error.
• Command-line arguments. There is a field for them above the input box, read through argc and argv.
• Extra compiler flags. You can add flags such as -Wall -Wextra, -O2, -std=c17 or -lm for gcc/g++.
• Multiple files. You can add, rename and delete files (for example main.c, list.c, list.h) and download all files from the Run dropdown. A project is limited to 200 KB in total and 100 KB per file.
• Saving. Save (Ctrl+S) stores the project in My Projects when you are logged in, with a project name and destination folder.
• Sharing. Share gives you either a Live Public Link that always shows your latest saved code, or a Share a Copy snapshot that expires after 1 day, 1 week, 1 month, or never ("Keep Forever"). Forever links need a login. The share dialog also gives you an Embed Code snippet for putting the editor on a web page or LMS.

Limits to know about

These numbers come from the OnlineGDB FAQ as of November 2026:

Limit	Value
Compile time	10 seconds
Run time, Text input mode	10 seconds
Run time, Interactive console	Until the program ends, or 15 minutes of inactivity
Memory	256 MB
Single file size	100 KB
Project size (all files)	200 KB
stdin, stdout, stderr	64 KB each (extra output is truncated)
Internet access from your program	None
Extra C/C++ libraries	ncurses, LAPACK

Other limits in practice:

• Debugger language coverage. The step debugger covers C, C++, Python 3 and Java. Other languages are run-only.
• Runtime exceeded. Infinite loops, unbounded recursion, very large data processing and missing stdin input all end with a runtime-exceeded error. The site's own error dialog lists exactly those four causes.
• Idle sessions stop. Run and debug consoles stop after inactivity ("Debug session is being stopped due to inactivity"), and a "Lost connection to server" message means you need to refresh the page.
• Old toolchains. gdb 12.1 and Python 3.8 are years behind upstream (GDB 18.1 shipped September 2026). Most coursework does not care, but very new language features may not work.
• No real project tooling. There is no CMake, no package manager and no way to install libraries. Anything beyond the standard library and a few files is better done locally.

Is OnlineGDB safe?

For learning and small experiments, yes, with sensible caution. Your program cannot reach the internet from OnlineGDB's servers, so a snippet cannot leak data out on its own. Your code itself, however, is stored on their servers when you save or share it. The site is ad-supported (ads were served via BuySellAds when we checked), and visitors in some regions see a consent dialog for advertising cookies, where Do not consent still lets you use the IDE. Nothing needs to be installed, so the site cannot change anything on your computer.

Is OnlineGDB down? Common messages and fixes

Message or symptom	What it means	Fix
"Lost connection to server"	Your browser lost its live connection to the run/debug server	Refresh the page. Save your code first if you can.
"New Version of OnlineGDB is available"	The site was updated while your tab was open	Save, then refresh.
"Debug session is being stopped due to inactivity"	No activity for about 15 minutes	Click Debug again.
Runtime exceeded / "Possible reasons for Runtime Exceed error"	Hit the time limit: loop, recursion, big data or missing input	Debug with pause, or give input via Text mode.
Output cut off	stdout/stderr passed 64 KB	Print less, or write a summary.
"connecting to server" never finishes	Network, VPN, firewall or ad blocker blocking the live connection	Try another network or browser profile, or disable extensions for the site.

If the page itself will not load from several networks, the site is likely having an outage, and waiting is the only fix. OnlineGDB's official X account is @onlinegdb.

OnlineGDB Classroom, premium and mobile

Classroom. OnlineGDB has a Classroom section (linked in the sidebar). According to the OnlineGDB docs, teachers can publish programming assignments to a class and evaluate and grade student submissions in several ways. It requires an account.

Premium. The only paid feature visible on the public site is ad removal: the Remove Ads button links to an upgrade page that asks you to log in or register. OnlineGDB does not list the premium price on any public page, so you will see it only after signing in.

Mobile. onlinegdb.com works in a mobile browser, but the editor and debug panels are cramped on a phone. App stores also carry apps named "onlinegdb": the App Store listing is free, advertises 39+ languages, custom compiler flags and interactive input, and names Aviraj Patel as the developer. The listings do not describe a step debugger, onlinegdb.com does not link to them, and some App Store reviews say they could not sign in to their OnlineGDB account, so treat them as separate apps.

OnlineGDB alternatives

No single online tool does everything. Here is how the main alternatives compare, with facts from each vendor's site as of November 2026:

Tool	Best for	Step debugger	Languages	Cost
OnlineGDB	Quick C/C++ debugging in a browser, classwork, sharing snippets	Yes: GDB for C/C++, pdb for Python, plus Java	47 menu entries	Free with ads, premium removes ads
JDoodle	Many languages, classroom use, embedding, a code-execution API	Yes: breakpoints and stepping; 5-minute sessions on Free, 15 on paid	114 languages, frameworks and databases	Free (1,000 runs/day); Student $4/mo, Pro $12/mo, Teacher $20/mo
Programiz	Beginners following tutorials	"Visualize" steps line by line and shows variables changing	18 languages	Free
OneCompiler	Quickly running code in many languages and databases	None advertised	110+ languages and databases	Free
Compiler Explorer	Seeing the assembly a compiler produces, comparing compilers and flags	No (it can execute code, but it does not step through it)	30+ languages, many compilers each	Free, open source (BSD-2-Clause), self-hostable
Replit	Full projects in a cloud workspace, AI agent, collaboration	Depends on language and setup	Many	Free Starter; Core $20/mo ($18/mo yearly), Pro $100/mo (pricing)
GitHub Codespaces	A full VS Code in the browser on a cloud Linux machine, with real gdb	Yes (VS Code debugger + gdb)	Anything you install	120 compute hours and 15 GB-month storage free per month on GitHub Free (docs)
Local gdb + VS Code	Serious debugging, large projects, any library	Yes	Anything	Free

JDoodle 114

OneCompiler 110+

OnlineGDB 47

Compiler Explorer 30+

Programiz 18

Counts as each site states them. OneCompiler and Compiler Explorer give minimums (110+, 30+). OnlineGDB counts menu entries, including separate C++ standards. Source: each vendor's site: jdoodle.com, onecompiler.com, onlinegdb.com, Compiler Explorer on GitHub, programiz.com

Language count is not the whole story. For C and C++ debugging, what matters is a real debugger with breakpoints, a call stack and a console you can type GDB commands into, and OnlineGDB, Codespaces and a local setup are the only options above that give you GDB itself.

If you are choosing a desktop editor to graduate to, DevHunt's comparison of popular IDEs covers VS Code, JetBrains IDEs and others. For JavaScript back ends, the equivalent guide is Node.js debuggers.

Local gdb in VS Code (the step up)

When you outgrow OnlineGDB, the same GDB debugger runs locally with a graphical front end. On Linux (or WSL on Windows), Microsoft's C/C++ debugging guide boils down to:

1. Install gcc/g++ and gdb, for example sudo apt install build-essential gdb on Ubuntu.
2. Install the C/C++ extension (ms-vscode.cpptools) in VS Code.
3. Open your .c or .cpp file, click in the margin (or press F9) to set a breakpoint.
4. From the drop-down next to the play button choose Debug C/C++ File, then C/C++: g++ build and debug active file.

VS Code writes a launch.json for you. The important parts are:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "C/C++: g++ build and debug active file",
      "type": "cppdbg",
      "request": "launch",
      "program": "${fileDirname}/${fileBasenameNoExtension}",
      "cwd": "${fileDirname}",
      "MIMode": "gdb",
      "miDebuggerPath": "/usr/bin/gdb",
      "preLaunchTask": "C/C++: g++ build active file"
    }
  ]
}

You get the same breakpoints, stepping, variables and call stack as OnlineGDB, plus conditional breakpoints in the UI, memory views and no limits on project size. On macOS, the default toolchain is clang with LLDB rather than gdb, which the same extension also supports. More options are in DevHunt's list of IDEs and code editors and open-source developer tools.

Plain gdb in a terminal

You do not need an IDE at all. The workflow that OnlineGDB wraps is four commands:

gcc -g -O0 -Wall main.c -o main   # -g adds debug info, -O0 keeps lines in order
gdb ./main
(gdb) break sum_to
(gdb) run

From there, every command in the cheat sheet above works the same. Type layout src (or start gdb with gdb -tui ./main) for a split view with your source code, which is the closest terminal equivalent to OnlineGDB's editor plus debug panels.

FAQ

Is OnlineGDB free?

Yes. You can compile, run and debug without paying or signing up. The free site shows ads; a paid premium option removes them. An account (free) is needed to save projects and create share links that never expire.

What does online GDB mean?

In short, online GDB means a GNU Debugger you use from a browser. GDB stands for the GNU Debugger, the standard debugger for C and C++ on Linux. "Online GDB" usually means OnlineGDB (onlinegdb.com), a website that runs gcc and GDB on its servers so you can compile and debug from a browser. Searches like "gdb online", "online gdb debugger" and common typos such as "online gbd" or "online gdp" all lead to the same site.

Can I debug Python on OnlineGDB (is there an online GDB for Python)?

Yes. Open the Online Python Debugger page or choose Python 3 in the language menu and click Debug; you get a pdb session paused on line 1 with Call Stack and Local Variables panels (tested November 2026). The interpreter is Python 3.8.10, so newer syntax such as match will not run. For modern Python, use VS Code with the Python extension or the built-in pdb locally.

What compiler does OnlineGDB use for C and C++?

It uses gcc 11.4.0 for C (in gnu99 mode by default) and g++ for C++: 11.4.0 for C++11 and C++14, 13.1.0 for C++17, C++20 and C++23, and 16.1.0 for C++26. The debugger is gdb 12.1, or gdb 17.1 for C++26. You can pick the standard from the language menu and add extra compiler flags.

What is an online GDB account?

It is a free OnlineGDB login created with Google, Facebook or GitHub (or a registered username and password). You don't need one to run or debug code. It lets you save projects in My Projects, organize them in folders, create share links that never expire, and use the Classroom features.

Why does my program show a runtime error on OnlineGDB?

The usual causes are an infinite loop, unbounded recursion, processing too much data for the server's limits (10 seconds in Text input mode, 256 MB of memory), or a program waiting on input you didn't provide. Check your loop conditions with a breakpoint or the pause button, and supply input in the console or switch Standard Input to Text.

Is OnlineGDB down?

Usually not. A "Lost connection to server" message means your browser lost its live connection, and refreshing the page fixes it. If "connecting to server" never finishes, a VPN, firewall or browser extension may be blocking the connection. If the site will not load at all from several networks, it is probably a real outage.

Is online GDB safe to use?

For learning and small snippets, yes. Programs cannot access the internet from its servers and nothing is installed on your computer. Do not paste secrets or proprietary code, because saved and shared code lives on OnlineGDB's servers, and Live Public Links can be opened by anyone with the URL.

How much is OnlineGDB premium?

OnlineGDB does not publish the price on a public page. The premium upgrade removes ads, and the upgrade page asks you to log in or register before showing details. Everything else (compiling, running, debugging, sharing) is free.

Does OnlineGDB have an API to execute code?

Not a documented public one. OnlineGDB's docs cover the IDE and Classroom only. If you need to run code from your own app, JDoodle sells a Compiler API, or you can self-host Compiler Explorer, which has a REST API.

Is there an OnlineGDB download or desktop app?

There is no official desktop app; OnlineGDB is a website. Third-party apps named "onlinegdb" exist in the App Store and Google Play, but onlinegdb.com does not link to them and their listings do not describe a step debugger. If you want the same debugger offline, install gcc and gdb locally and use them from the terminal or through VS Code, as shown above.

What are the best OnlineGDB alternatives?

For C and C++ debugging in a browser, GitHub Codespaces gives you real gdb in VS Code. JDoodle has more languages and a step debugger, Programiz is friendliest for beginners, OneCompiler covers 110+ languages for quick runs, and Compiler Explorer is the tool for inspecting assembly. For serious work, gdb with VS Code on your own machine is free and has no limits.