OneCompiler API: key, pricing, and an alternative that judges

The short answer

• Stay with OneCompiler if you need a language outside our 46, stdin beyond 100 KB (we cap input there; it allows 1,000,000 characters), or its embeds (editor, challenges and interviews) from the same vendor.
• Switch to OnlineCompiler.io if you want to check output against expected answers (verdicts, hidden tests, scores), a free plan that renews with 100,000 runs a month, a price per run you can work out, or Judge0- and Piston-compatible endpoints.

What does the OneCompiler API offer?

From OneCompiler's code execution API page and APIs page, checked on 6 November 2026:

• One POST endpoint, https://api.onecompiler.com/v1/run, with the key in an X-API-Key header.
• "110+" languages, including web and database types, listed by id.
• Several files per program, and stdin as a single value or an array: with an array the code runs once per value and you get an array of results.
• Stdin up to 1,000,000 characters, with extra stdin billed per additional 100,000 characters.
• A response with stdout, stderr, exception, compilationTime, executionTime (ms), memoryUsed (KB) and the credits left.
• Error codes such as E001 (timed out) and E002 (quota exceeded).
• Embeds from the same vendor: an editor, coding challenges, a studio and AI interviews.

How do I get a OneCompiler API key?

OneCompiler says keys are created in its API Console, which also manages credits and shows usage. Its pages give no further steps. On OnlineCompiler.io a key is free to create, with no card, and a key can have its own monthly limit.

What does the OneCompiler API cost?

On its page, checked 6 November 2026:

• $1 buys 2,000 credits; $100 or more buys 2x credits (4,000 a dollar); $500 or more buys 3x (6,000 a dollar).
• New accounts get 100 free credits.
• Credits per run are not stated, and the API tab of its pricing page showed no figures.

Ours is plain: the Free plan is 100,000 runs a month, and Pro is $49 a month for 1,000,000 runs, $0.049 per 1,000 at full use. Prepaid credits suit a project with occasional bursts; a monthly plan suits steady use.

Feature by feature

How do I move a OneCompiler call?

OneCompiler's run endpoint is synchronous, and so is ours. Keep the key on your server. The same program, in both shapes. The second was run on 6 November 2026 and returned the result below it.

curl -X POST https://api.onecompiler.com/v1/run \
  -H "X-API-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "language": "python",
    "stdin": "Peter",
    "files": [
      {
        "name": "main.py",
        "content": "import sys\nname = sys.stdin.readline().strip()\nprint(\"Hello \" + name)"
      }
    ]
  }'

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": "import sys\nname = sys.stdin.readline().strip()\nprint(\"Hello \" + name)",
    "input": "Peter"
  }'

{
  "status": "success",
  "exit_code": 0,
  "output": "Hello Peter\n",
  "error": ""
}

What if I want to check the output?

With a stdin array you get every output and compare them yourself. Here the same program is judged in one request, with one hidden test. Each test returns a verdict such as accepted or wrong_answer, and the response has a score and a signed receipt. The program was run on both inputs in the sandbox on 6 November 2026: it printed Hello Peter and Hello Ann, each with a newline, so both tests pass.

curl -X POST https://api.onlinecompiler.io/api/run-tests/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "python-3.14",
    "code": "import sys\nname = sys.stdin.readline().strip()\nprint(\"Hello \" + name)",
    "tests": [
      {"input": "Peter", "expected_output": "Hello Peter\n"},
      {"input": "Ann", "expected_output": "Hello Ann\n", "hidden": true}
    ]
  }'

Tests can be kept on the server as a stored problem and judged by id, with results kept for 90 days on the Free plan. See how to build an online judge and the wider comparison of code execution APIs; free tiers are compared in free code execution APIs.

Frequently asked questions

How do I get a OneCompiler API key?

OneCompiler says keys are created in its API Console, where you also manage credits and watch usage (its APIs page, checked 6 November 2026). You send the key in an X-API-Key header. For ours, create a key on the API keys page; it is free, needs no card, and goes in an Authorization header.

How much does the OneCompiler API cost?

Its code execution page lists prepaid credits: $1 buys 2,000, $100 or more buys double, $500 or more triple, and a new account gets 100 free credits (checked 6 November 2026). It does not say how many credits one run uses, and the API tab on its pricing page showed no figures, so the cost of a run cannot be worked out from its pages.

Is the OneCompiler API free?

Only as a trial: new accounts start with 100 credits. OnlineCompiler.io's free plan is 100,000 runs a month with commercial use allowed, no card, and a monthly limit that renews.

Can I check output against expected answers with the OneCompiler API?

Its API runs the code once per stdin value and returns each output, but the pages describe no expected output, verdict or score, so you compare outputs yourself. OnlineCompiler.io judges in the same request: send tests with expected outputs, mark some hidden, and get a verdict per test and a score.

Can I keep my Judge0 or Piston code and move off OneCompiler?

Yes. OnlineCompiler.io has Judge0- and Piston-compatible endpoints, so code written against either keeps its requests and changes only the base URL and key. OneCompiler has its own request format, so that move means changing the request, as in the example above.