Free Compiler Online
Run Python, JavaScript, C++, and SQL code in sandboxed environments. Useful for testing snippets, learning, prototyping algorithms, and explaining code without setting up a local environment.
4 free tools — browser-based, no sign-up required.
Python Compiler
NEWWrite and run Python code online
JavaScript Runner
NEWRun JavaScript code online instantly
C++ Compiler
NEWCompile and run C++ code online
SQL Runner
NEWRun SQL queries online with SQLite
About FlexyPdf Compiler
The online compilers are designed for short snippets — testing an algorithm, checking syntax, exploring a library function, running a small SQL query — not for long-running production workloads. Code is executed in a Docker-sandboxed environment with strict CPU, memory, and time limits, which keeps execution safe and prevents one user's code from affecting others. The trade-off is that you cannot install arbitrary packages or run interactive REPLs that wait for stdin.
Python runs Python 3 with a curated set of common libraries pre-installed (NumPy, Pandas, requests, the standard library, and the most common data-science packages). JavaScript executes as Node.js with current LTS features. C++ uses g++ with C++17 enabled, suitable for competitive programming and algorithm exercises. SQL runs against an in-memory SQLite database, which means you can CREATE TABLE, INSERT, and SELECT within a single session — useful for testing query logic without a real database.
The runners are intended for learning, prototyping, code snippets in tutorials, and quick verification of algorithms. They are not a substitute for a proper development environment, do not retain state between runs, and do not accept interactive user input mid-execution. For longer-running or stateful work, set up the language locally — every supported language is free to install.
Who uses these tools
A few of the recurring use cases we hear about from FlexyPdf visitors.
Students and self-learners
Running Python homework problems, testing C++ competitive programming solutions, exploring SQL queries against sample data.
Interviewers and candidates
Sharing a runnable code snippet during a technical interview, verifying a solution before pasting it back to the interviewer.
Tutorial authors and educators
Embedding runnable code examples in articles, testing snippets before publishing.
Working developers
Sanity-checking a small algorithm in a language you don't have installed locally, running a quick SQL query without spinning up a database.
Frequently asked questions
Is the sandbox secure against malicious code?
Each execution runs in an isolated Docker container with no network access, restricted filesystem, capped CPU/memory/time, and is destroyed after completion. The sandbox is designed to contain malicious or buggy code safely.
Can I install Python packages or npm modules?
No. The runners use a fixed set of pre-installed packages (the common ones for each language) and do not allow on-the-fly installs. This keeps execution fast and avoids supply-chain risks. If you need a specific package, run the code locally.
Why does my code time out?
Each execution is capped at a short wall-clock time (a few seconds) and a fixed memory limit. Infinite loops, very large allocations, and CPU-intensive algorithms will hit those limits. The limits are intentional — the runners are for small snippets, not workloads.