Online XPath evaluator and querySelectorAll tester for HTML/XML — instant match count, real highlighting, and copy-as-code for Scrapy, Selenium and Playwright.
Online C sandbox — compile and run C with GCC 10.2 in your browser. Pick C89/C99/C11/C17, toggle -Werror, add flags (-Wall -O2 -lm), feed stdin. Zero install.
Run Python 3 in your browser via Pyodide (CPython on WebAssembly). Full stdlib, pip via micropip, persistent session, offline after first load. Zero install.