Free code execution APIs
Free code execution APIs in 2026: what each free tier gives you
The largest free tier among hosted code execution APIs is OnlineCompiler.io's, at 100,000 runs a month with commercial use. JDoodle gives 20 runs a day, Codapi's cloud 1,000 a month and OneCompiler 100 credits once, while hosted Judge0 and Sphere Engine have no free plan. Judge0 and Piston are free to host yourself.
By the OnlineCompiler.io team. Updated . We make OnlineCompiler.io, so we're one of the options here. Every competitor figure links to the vendor's own page, and we say where our API falls short.
Free tiers compared
| Service | Free allowance | Roughly per month | Paid from | Judging |
|---|---|---|---|---|
| OnlineCompiler.io | 100,000 runs a month, commercial use included | 100,000 | $10 a month for 150,000 runs | A verdict per test, hidden tests, scoring |
| Codapi (cloud) | 1,000 runs a month, no sign-up | 1,000 | $5 a month for 5,000 runs | No |
| JDoodle | 20 runs a day | About 600 | $10 a month for 1,000 runs a day | No |
| OneCompiler | 100 credits, once | 100 in total | $1 for 2,000 credits | No (batch stdin) |
| Judge0 (hosted) | None at checkout (50 a day advertised) | 0 | $44.99 a month on RapidAPI for 2,000 runs a day (€27 list price) | One expected output per submission |
| Sphere Engine | 14-day trial | 0 after the trial | Quote only | Stored problems, in the separate Problems module |
| Piston (public API) | Whitelist only since 15 February 2026 | 0 for most projects | Self-host only | No |
Daily quotas matter more than they look: JDoodle and hosted Judge0 count runs per day, so a class or contest that runs everything on one evening can hit the cap while most of the month goes unused. A monthly allowance absorbs the spike.
Free to host yourself
- Judge0 (GPL-3.0) has judging built in, but needs cgroup v1 and privileged containers, which modern Ubuntu, WSL2 and managed Kubernetes don't give by default. Moving off a self-hosted Judge0 is covered in migrating from Judge0.
- Piston (MIT) has 84 languages and no judging. If your app called the public API, see the Piston API alternatives.
- Codapi (Apache-2.0) is aimed at runnable examples in docs.
The software is free; the servers, security patches and time to run them are not. For a side project that may still be the right trade.
What to check in a free tier
- Commercial use: some free tiers are for evaluation or personal projects only.
- Daily or monthly quota: monthly allowances survive deadline spikes.
- Judging: whether it can compare output with test cases, or you write that yourself.
- Published limits: time, memory and output size per run, so you know what students hit.
- Isolation: what the sandbox is, and whether programs get network access.
- Language versions: Python 3.14 and Java 25, or versions from years ago.
Try a free code execution API in one request
Get a free key by signing in, then run this. The output comes back in the response, along with any errors, the exit code, run time and memory:
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": "print(int(input()) * 2)", "input": "21"}'The same key works for all 45 languages, the run tests API, the Judge0 and Piston endpoints and the MCP server, and the same free allowance covers the embeddable editor. The full comparison, paid plans included, is in Judge0 alternatives.
Frequently asked questions
What is the best free code execution API?
For the most free runs, OnlineCompiler.io: 100,000 a month in 45 languages, commercial use included, with test-case judging and Judge0- and Piston-compatible endpoints. JDoodle (20 runs a day) and Codapi (1,000 a month) suit lighter use. Judge0 and Piston are free only if you host them yourself.
Is there a free online compiler API for Python, Java or C++?
Yes. OnlineCompiler.io's free plan runs Python 3.14, Java 25, C++ (G++ 15) and 42 other languages through one endpoint and one key, up to 100,000 runs a month.
Is Judge0 free?
Self-hosted Judge0 is free under GPL-3.0, but you run the servers, and it needs cgroup v1 and privileged containers. Hosted Judge0 offered no free plan at checkout on 18 October 2026; RapidAPI plans start at $44.99 a month for 2,000 runs a day.
Is the JDoodle API free?
Yes, up to 20 credits a day, and a run costs one credit. Paid plans start at $10 a month for 1,000 credits a day.
Can I use a free code execution API in a commercial product?
OnlineCompiler.io's free plan allows commercial use. For other services, check their terms: free tiers are often meant for evaluation or personal projects, and Piston's public API now serves only non-commercial educational projects.
What happens when I run out of free runs?
On OnlineCompiler.io, runs over the allowance get HTTP 429 until it resets at the start of the next month (UTC), and nothing is billed. We email you at 80% and 100%. Paid plans start at $10 a month for 150,000 runs; Pro is $49 for 1,000,000, or $0.049 per 1,000.