Should I use the sync or the async endpoint?

Use /api/run-code-sync/ when you can wait for the result in the same request: it returns when the run ends, within 30 seconds, and answers 429 when your account's runs at once are all busy. Use /api/run-code/ to queue runs: it answers 202 at once, waits for a free sandbox and POSTs each result to your callback URL.

How do I send input to the program?

Send it as input, up to 100 KB: the program reads it as standard input. SQL is the exception, because SQLite reads the program from standard input; there the script reads input with readfile('input').

What do exit codes 124, 137, 153 and 71 mean?

124: the run went over its time_limit, or compiling and running together went over 30 seconds. 137 (signal 9): the program was killed at the 512 MB memory limit. 153 (signal 25): it printed more than 8 MB. 71: it had more than 16 processes running at once, so the sandbox stopped; error says so. Other codes come from the program itself, such as 1 for an uncaught Python exception.

Docs

Run code: get a program's output, errors and exit code

POST source code, a compiler id and optional input. /api/run-code-sync/ waits for the run and returns its output, errors, exit code, run time and memory in the response; /api/run-code/ answers at once and POSTs the same result to the callback URL on your API key.

Run Code (Sync)

New

Execute code and get results in a single request. No callback URL needed: the response contains the execution output directly. Ideal for simple integrations, scripts, and AI agents.

POST /api/run-code-sync/

Request Body

Parameter	Type	Required	Description
compiler	string	Yes	Compiler identifier (see list below)
code	string	Yes	Source code to execute (max 100KB)
input	string	No	Standard input for the program (max 100KB)
time_limit	number	No	Seconds the program may run, above 0 and up to 30. The run is stopped at this limit with exit code 124; compiling before it does not count, but Java, Groovy and F# get a start-up allowance on top. Without it, the run gets what is left of the 30-second timeout.

Response (200)

Response

{
  "output": "Hello, World!\n",
  "error": "",
  "status": "success",
  "exit_code": 0,
  "signal": null,
  "truncated": false,
  "time": "0.0248",
  "total": "0.0330",
  "memory": "8192"
}

Examples

Terminal

curl -X POST https://api.onlinecompiler.io/api/run-code-sync/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "python-3.14",
    "code": "name = input()\nprint(f\"Hello, {name}!\")",
    "input": "World"
  }'

Note: The sync endpoint blocks until execution completes (up to 30 seconds). For high-throughput or long-running code, use the async endpoint or WebSocket instead.

Run Code (Async)

POST /api/run-code/

Request Body

Parameter	Type	Required	Description
compiler	string	Yes	Compiler identifier (see list below)
code	string	Yes	Source code to execute (max 100KB)
input	string	No	Standard input for the program (max 100KB)
time_limit	number	No	Seconds the program may run, above 0 and up to 30. The run is stopped at this limit with exit code 124; compiling before it does not count, but Java, Groovy and F# get a start-up allowance on top. Without it, the run gets what is left of the 30-second timeout.
extra_params	object	No	JSON object returned in the callback (max 8KB)

Async execution: The API returns 202 Accepted immediately with a queue ID. Results are delivered to your API key's redirect URL as a POST callback. Use a public HTTP(S) URL; private addresses, embedded credentials, and HTTP redirects are not supported.

Code Examples

Terminal

curl -X POST https://api.onlinecompiler.io/api/run-code/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "python-3.14",
    "code": "name = input()\nprint(f\"Hello, {name}!\")",
    "input": "World"
  }'

Response

Immediate Response (202)

Response

{ "status": "queued", "id": 42 }

Callback POST Body

Once execution completes, results are POSTed to your API key's redirect URL:

Callback Payload

{
  "output": "Hello, World!\n",
  "error": "",
  "status": "success",
  "exit_code": 0,
  "signal": null,
  "truncated": false,
  "time": "0.0248",
  "total": "0.0330",
  "memory": "8192",
  "time_limit": 30,
  "extra_params": {}
}

Field	Description
output	Standard output (up to 64 KB; NUL and invalid UTF-8 bytes come back as U+FFFD)
error	Standard error / compilation errors (up to 64 KB; NUL and invalid UTF-8 bytes come back as U+FFFD)
status	"success" or "error"
exit_code	Process exit code (0 = success)
signal	Signal number if killed (e.g. 9 for SIGKILL), null otherwise
truncated	true if output or error went over 64 KB and was cut
time	Run-command wall time in seconds; includes the compilation Java, F#, Deno, Dart, Erlang, Elixir, Clojure, Groovy and Racket do as they run
total	Script wall time in seconds, including separate compilation; excludes container startup
memory	Memory usage in KB
time_limit	The run's time limit in seconds: yours, or 30 without one
extra_params	Your custom data, passed through unchanged

Exit Codes & Signals

The exit_code field contains the process exit code. A value of 0 means the program ran successfully. Any non-zero value indicates an error.

When exit_code is greater than 128, the process was killed by a signal. The signal field provides the signal number (i.e. exit_code - 128). When the process exits normally, signal is null.

Exit Code	Signal	Meaning
0	null	Success
1	null	Runtime error (e.g. uncaught exception, assertion failure)
2	null	Misuse of command / invalid arguments
137	9 (SIGKILL)	Killed: over the 512 MB memory limit
139	11 (SIGSEGV)	Segmentation fault: invalid memory access
124	null	Timeout: the run went over your `time_limit` (plus the start-up allowance for Java, Groovy and F#), or compile and run together went over 30 seconds
153	25 (SIGXFSZ)	Stopped for flooding output: more than 8 MB across both streams
71	null	Too many processes: more than 16 running at once, so the sandbox stopped. Output printed before that is kept, and `error` says what happened

Questions

Should I use the sync or the async endpoint?: Use /api/run-code-sync/ when you can wait for the result in the same request: it returns when the run ends, within 30 seconds, and answers 429 when your account's runs at once are all busy. Use /api/run-code/ to queue runs: it answers 202 at once, waits for a free sandbox and POSTs each result to your callback URL.
How do I send input to the program?: Send it as input, up to 100 KB: the program reads it as standard input. SQL is the exception, because SQLite reads the program from standard input; there the script reads input with readfile('input').
What do exit codes 124, 137, 153 and 71 mean?: 124: the run went over its time_limit, or compiling and running together went over 30 seconds. 137 (signal 9): the program was killed at the 512 MB memory limit. 153 (signal 25): it printed more than 8 MB. 71: it had more than 16 processes running at once, so the sandbox stopped; error says so. Other codes come from the program itself, such as 1 for an uncaught Python exception.